When you have everything in the game on farm and are trying to speed things up, the need for shadow priests drops, obviously. But I've yet to hear a mage saying he can last through a fight without a shadow priest during progression with the exception of very short fights. In fact, the mages in my old guild that just downed illidan use mana pots sometimes even with a shadow priest.
I wouldn't look at a 3 minute gorefiend as your baseline... Not to mention the length of the fight / amount of extra mana you have has an effect on how much dps you'd gain with extra mana. The more spare mana you have the less ineffective mana restoring methods you're using, and thus additional mana will only allow you to drop the more effective methods of mana restoration.
For example, a mage with no extra mana would restore mana by wanding. This is very bad.
If he has mana to never wand and gets more mana, he'll swap his resto shaman to an elemental shaman, which is a decent dps increase compared to the mana lost.
If he still has mana left over, he'll drop his evocation or shorten it.
If after not using evocation at all he still has too much mana, he'll drop gems for flame caps.
If he still has too much mana after not using any mana gems he'll use destruction potions.
After that additional mana is useless (unless I missed something on the way).
Warlocks have less options - first they will stop life tapping and then if they still have too much they'll use destruction potions.
What you need to compare is what kind of consumeable swaps (and how many of them) would happen if you give the warlock more mana vs the mage, and which ones will provide more damage to your raid. This isn't a simple calculation at all in short fights! But in long fights the mage reaches the "wand" point without a shadow priest so he should clearly have it for those.

I might add that as T4/T5 Elemental Shaman I've no real mana issue. It is to the degree that I tend to use Lightning Shield instead of Water Shield during raid trash. A Shadow Priest in your party, and you will end the fight with more or less a full mana bar. Without a Shadow Priest and you'll need to drink 1-3 Mana Potions during boss encounters.

How should I put it ... I use mana pots every 2 minutes in every fight since I've started using pots, this is not dependant on group I'm in and I'm pretty much all the time with spriest and resto shaman.
If a mage has to evo once in a 10 min fight while chaining mana pots out of spriest group I have to Life Tap for around 60-70 seconds out of 10 minutes while chaining pots. My dps simply doesn't stand a chance compared to a mage if he has support and I have minimal support.

If it was me doing he groups I'd give mages crit (moonkin, ele) and locks regen (resto shammy, spriest). They'll all be using mana pots every cooldown anyway if they're serious about their dps, if they're not they can rot outside the instance for all I care. Try to get 2 shadow priests though and give everyone what they need. Makes for some nice flexibility in healing intensive fights where you want some healers with regen and not letting casters mana starved.

In the end it's who gives you most consistent top dps that should get most support but be careful how you judge that.

Rule 1 :- Never compromise your SPriest's damage unless known to be threat capped. Every extra bit of damage results in more mana for that party. Extra Crit buffs are not vital, but they help. Moonkins are unviable without an SPriest anyway imo. The SPriest has as much a problem with mana as Oomkins do and the more mana they get back the longer the SPriest can keep on providing mana for the rest. They typically chain pot in most encounters anyway. If they have to back off their damage to save mana they reduce the mana return to all. Help them.

Rule 2 :- There is nothing more calamitous than all healers going Oom. Putting 2 or 3 healers in an SPriest group can return enough mana on endurance encounters to enable you to swap in another dps to shorten the encounter. This is not so much the case in encounters where healing per second is the driver rather than lasting power. If healers are fine and/or you are over-weight in healers then put Moonkins, Mages or Elemental Shamans in the group. They can't dps without mana.

I would build the group around the SPriest :-

SPriest
Resto Shaman (Wrath of Air, Mana Tide, Improved Mana Spring)
Moonkin / Healer / Mage / Ele Shammy
Healer / Mage
Healer / Mage

I can't see why you would put a Warlock in an SPriest group as standard. All of their buffs other than VT and VE are not party specific (ISB, Misery, Curse of Shadows, Shadow Weaving). The healing from VE is irrelavant in most encounters (it can be replaced by a Renew or other HoTs for the Lock) and the threat created by it is very relevant in most encounters.

Ideally you would have more than one SPriest anyhow.

I can see that I was obviosly wrong on the shadowpriest thing and their DPS boost to mages, locks etc.
That's fine, as I mentioned im not a caster and nor do I setup raid for caster DPS..

But I still think that an enchancement shaman is far superior (in raidDPS) than an elemental shaman is. Windfury + str totem + 10% AP vs 100 spelldamage and 3%crit (assuming hit capped). Some suggest that it's only a matter of improved WF and str + 10% AP - but then a resto shaman would ofc have to be put in a melee group, wasting their own buffs, and not benefitting from battleshout etc etc.

Our castergroups are normally 3x mage, 1 lock, 1 resto shaman. and second maybe 1 lock, resto shaman, Spriest, 2x healers or something like that. Maybe the Spriest is better off in the mage group? I wouldn't know, what do you think?
anyway our melee groups is clearly buffing eachother perfectly too this way, having 1 ench shaman, 2 x war, feral, sword rogue and second: feral, 3x hunter, dagger rogue. this way no buffs are "wasted", as they would be if the ench shaman was replaced by a resto.

It ofc depends on the raidmembers also - our melee tend to do alot more damage than casters. and buffing them seems to overall give a greater boost, than buffing casters. As far as I can see from our WWS our casters get buffed with 100-150 dps with elementalshaman, whereas fury warriors get buffed with almost 300 dps, and sword rogues 200-250 dps from an enchancement shaman. We do use shadowpriests and I'm gonna try sticking them in castergroups instead of healinggroups whenever healing isn't so tough, see if it benefits us more.

Oliria, this is not a debate involving enhancement shaman at all, so please stop bringing it up. This isn't a debate about the viability of talent specs or classes, it is assuming we are using them, so please try to make your posts consider that point. Notice the title of the thread is Best use of caster-buffing classes, and the original post says he has an elemental shaman, a boomkin and an spriest who will be there.

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I've seen that our elemental shaman never runs OOM when in a shadow priest group. It doesn't look like he even loses mana. The spriest doesn't really benefit the elemental shaman then, however the spriest demands the elemental shaman whenever he is in the raid. Unfortunately I cannot say whether that is for personal dps marks or the mana gain of 3% crit being greater than the mana gain of mana tide.

I think what it comes down to is gearing. Mages and Warlocks are both going to get significant buffs from being with the Hybrids, and therefore you should probably stack your best geared altogether, as due to scaling buffing the most geared is more dps than buffing the least.

Just the fact that your melee group is buffing eachother perfectly doesn't automatically mean it's good. If your enhancement shaman is doing shitty dps you're better off with a good hunter/mage/lock and put a resto shaman for the windufury.

Also if the fight is long enough for your healers to oom, it's also long enough for your mages to oom. Take away the mages' shadow priest and your healers can last longer but the fight will also take longer - you will probably benefit more by putting the shadowpriest with the mana starved dpsers first, other dpsers later and healers last, with the exception being an extremely healing intensive fight (where you're possibly low on healers) where the 2nd shadow priest should go with healers insetad of hunters/warlocks.

Buffing the shadow priest to the max is nice and all, but if his mana goes to people who don't need it as badly you've not really gained anything.

Best is to have 3 shadow priests, of course, so everyone can go crazy on dps and healing and finish the fight faster with less deaths. If you don't have that option, though, the first SP should go to mana starved DPSers.

All mana users would like to have unlimited mana. The thing with locks is that they have an additional method of getting mana through life tap that is limitless as long as there are healers around with mana. That is priceless. Buffs to help the warlocks should be damage/crit based imo, but any surplus mana producers (Spriests, resto shammies etc) always help.

We are all making sweeping generalisations here. So many things should be taken into account relative to the gear spec and endurance of each mana user in the context of the next boss encounter.

I will surely take that in to considaration - never thought that casters would benefit that much from a shadowpriest, so it's nice to get some info on that. I know it's offtopic, and im sry for that, but for the record our ench shaman is doing top3-5 damage. (reply to galzohar)

So the general belief is that Spriest go to mage groups with a moonkin if one is used, rather than warlocks and elemental shamans?

The biggest thing a Shadow Priest does for an elemental shaman is allow us to change our consumables and spell rotation. If I don't have a shadow priest, I tend to stick with LB spam and drinking mana potions. I won't run out of mana this way. However, when I get a shadow priest, I can do two things:

1) Chain chug destro pots
2) Change my rotation from LB spam to LBx3, CLx1. This is a significant dps boost, but it is very inefficient.

We generally run with two shadow priests (with one being significantly stronger than the other two). We are 4/5 Hyjal and 4/9 BT for reference. I used to run with one shadow priest with healers, but after a while, I saw how much damage our hunters were doing, and considering that they were limited by mana, I moved the second shadow priest out of the healer group and into a second dps group. The only fight so far where I need healers with SP's is Bloodboil (we've only had 1 attempt on him - still learning it, so I can't give any input on later fights or that one as a farmed boss).

Due to how our guild does rotations, we either have me as the only elemental shaman or we have a second. We also have 2 hunters in each raid (spec varies based on the hunter)

The groups I generally run are:

Group 1
1) Strongest SP
2) Ele Shaman (me)
Depending on raid makeup:
3) Moonkin (if we have one in the raid), Destro lock (if we have one in the raid), BM hunter (if not the others)
4) Mage
5) Mage

Group 2
1) Weaker SP
2) Elemental shaman (if he's in the raid), Warlock or Hunter if not
3) Warlock or Hunter
4) Warlock or Hunter
5) Warlock or Hunter

This second group usually ends up as either:
SP, Ele Sham, Hunter, Hunter, Warlock
SP, Ele Sham, Hunter, Warlock, Warlock
SP, Hunter, Hunter, Warlock, Warlock

The SP in the second group won't always get the maximum benefit from their group, but the rest of the group will always benefit from them. If your hunters know what they are doing, and are high enough dps, that justifies giving them a SP as well.

The synergy between the moonkin, mages, myself, and the strongest shadow priest is phenomenal, as is the synergy of a BM hunter in there instead of the moonkin.

Your setup would work extremely well with a 2nd Spriest...

Grp1:
Spriest
Mage
Mage
Mage
Resto Sham

Grp2:
Destro Lock
Destro Lock
Ele Sham
Moonkin
Spriest

Mages get Mana Tide and Spring, and Locks get full crit buffs. Swap the Mages for the Locks at 20% and Bloodlust.

I know this isn't what you mentioned, but food for thought, as you have near amazing caster synergy if you can nab another Mana Battery.

Obviously 2>1 ;p

I would say this is probably optimal.

Melee dps can finish the fight, but can you finish the fight without healers?

By the way... are you people considering the moonkin with 4 warlocks means more ISB up-time, which increases the damage of ALL warlocks/shadow priests?

With four warlocks in T6 gear, Improved Shadow Bolt is pretty much always up anyway. Taking the uptime from 85% to 87% isn't that much of an increase.

You have any evidence of this? Simulations rarely show more than 55-60% uptime in your average t6 raid.

What you just said is pretty much impossible, unless your raid is stacked pretty weirdly.

Thus far, everyone in this thread has been dissecting the question from the PoV of the mages/locks. You quickly learn the right setup when you view things from the PoV of the buffing classes themselves.

What does a spriest/aff lock want anything to do with crit? (Destro locks as well have DoTs that account for more of their dps than a fire mage's passive DoTs etc)
By the same token, what does an ele sham want? What does a boomkin want?

We've established that everyone wants more mana regen. We've established that everyone wants more crit/dmg/regen.

Make one group a 'crit' group with a resto sham for regen.
Make one group a 'dmg' group with the spriest for regen.

Umm destro locks don't use dots in T6 0/21/40 builds. All they do is spam shadowbolt non stop. Using any dot such as corruption or coa or whatever is a dps downgrade for them.

The point is pretty clear. Boomkins, mages and ele shamans have to have a sp. Otherwise they just really aren't viable. Warlocks don't necessarily have to have them due to lifetap and healers mana. So even though they can definitely use the crit bonuses, they often get thrown in weird groups. Now if you are past the progression mode and all you care about is maximum dps then well mana isn't a concern anymore. At that point put the destro locks in with the ele shaman and boomkin for massive dps. At this point a SP for caster mana doesn't really matter, since the fight is taking less than 4 minutes in all likelihood anyway.

I knew 4pc t6 was huge; I didn't know it changed rotations to a point of simple SBolt spam. Disregard my former post.

It's not the gear; it's the build. The 0/21/40 build was good even midway through SSC if you had enough crit, since it scales better than affliction or demonology.

True, but before 4pc T6, you should still cast Immo/Corr. Their DPCT is still higher than SB, assuming a fire mage in the raid. If no Fire mage, and no fire talents, drop Immo unless it's a movement fight.

After 4 pc T6, you should definitely drop Immo, and probably drop Corr.