The resistance cap (415, which is all 3 armor pieces and an aura/totem) is at 75% average mitigation; I believe it's roughly linear scaling from there down to zero. Sapphiron is a sufficiently long fight for a guild learning it that you probably need the mana help, to say nothing of people inevitably not noticing blizzards or taking splash damage for ice blocks or whatever.

For Sapphiron my healing strategy is very similar to those that have been posted. A major difference I would say is that I PW:S dpsers that tend to stand in blizzards for a bit too long. I'm also running the PW:S glyph so it helps out with this. It can help out some to use PW:S if its just one person or two but really people can't really stand in blizzards. For the most part I just bounce PoM, Flash Heal, CoH behind blocks, and I toss a binding heal on someone if I get too low and PoM is on cooldown.

Generally do not have mana problems during this fight because PoM is so awesome for this kind of damage.

10 man malygos: We seem to get phase 1 fine but run out of steam during phase 2. We had a warrior MT and druid OT with 1 DK bringing mobs to sparks every other time(cooldown limiting?). We had 1 holy priest and resto druid on MT/OT and myself(holy) on raid. Its hard to tell if we just arent getting into the sparks fast enough or if we need better gear/mana regen for healers. May spec into spirit buff in disc for this fight if raid healing...Any suggestions? If i recall we only had one replenishment class.

You might try swapping yourself onto the Sartharion tank (feral I presume?). We two-healed it with myself and a Paladin and our initial healing strategy sounds similar to yours; the Paladin had beacon on the drake tank and focused his attention on the Sartharion tank, while I focused on the drake tank, the adds tank, and Torment raid healing (also, do you have a separate tank for adds or is the Warrior grabbing those as well?). We had some issues with the drake tank dying, and realized that it usually happened when the Sarth tank and drake tank were out of beacon range, leaving me stuck trying to power through the spikes you describe by myself.

We did two things to fix that. First, the Sarth tank became my priority and the Paladin focused on the drake tank with beacon on the add tank. Damage on the Sarth tank isn't actually that bad, outside of the breaths, so as long as I kept him topped off before breaths and made him survive the next melee swing after, the Paladin could help me refill him at his leisure. We also slowly work our drake tank from the Tenebron landing area over towards the Sarth tank as the fight goes on, so that eventually they're sharing the same gap for waves from the south. Once our raid is all together like that, the Paladin has a lot more flexibility in moving beacon around according to the demands on each tank.

Well Trouble what will really happen is we will cast 'somewhat' in cycles. You will CoH everytime you can, and PoM everytime you can. In between it is really going to be filled with flash heals. I'm currently not spec'd for surge of light, but come the cooldown era, I may have to go back (though I don't like it).

I honestly don't see it effecting you guys as much I mean, your WG heals will get more effectiveness now and won't just be overwritten by CoH. I'd expect to see more complimentary raid healing on fights like Sapph, Sarth-3D, and Malygos for sure. I think it will bring the biggest change to the concept that holy priests are the premiere raid healers and will bring us more in line with the versatile 'can-do-everything' healer.

I for one am happy that they are changing the spell, it needed a fix. However, I think the cooldown was a poor choice and was just the easiest way out.

Intuitively I would say none. We are currently sniping so many heals with CoH that druids and shamans basically have altered their healing because of them only ending up overhealing anyway. With the nerf I would expect CoH to be used as an instant stabilizer and CH and WG to be used for topping people up. Meanwhile priests will have PoM and instant Flash Heals that can be used on critical targets.

All the cases where some priests say CoH needs to be spammed (vortex, sapph, KT ice blast) should be managable with the tools a raid has, even if all fights are left unchanged. I don't see any current boss fight causing trouble. The trash pull before Gothik may be hard though.

I may be overly optimistic though, but I see a lot of untapped healing potential from shamans and druids currently.

Just to add a few things to the other answers:

The short answer is, it depends on how your priests currently heal. If they rely heavily on CoH to the exclusion of other spells in most circumstances, you will notice more healing for you and other healers to do. If your priests don't use CoH that frequently right now, you will likely not see much difference at all.

The couple occasions I do see it affecting healing (such as melee ice blocks on KT), raid positioning is likely to get at least some of the blame. Being able to keep every melee alive as they chain ice blocks all around KT was almost certainly not intended to be healed through anyway. I expect some dps will have to learn better positional awareness for those fights.

I have to agree that I am glad CoH is being modified, although the cooldown is not a solution I truly appreciate as it feels more like a "governor" than a reason for priests to consider other spells.

We use CoH mainly because ... well, it's cheap, it's effective, and it's something to do. We can't effectively compete on tank healing (esp. trash, but also bosses) when paladins can spam HL for more healing and less mana cost. So we raid heal, and CoH is the premiere raid healing tool in the game until the nerf hits.

I just wish they'd gone to *anything* but a cooldown-based nerf. Watching a 6 second and 7 second cooldown is going to be exceptionally annoying. With Renew in its current state, it's basically going to be a set cycle: CoH, PoM, Flash, <gcd-ish for whatever you want, including another Flash, or a GHeal, or just standing>, rinse, repeat.

They could have solved the problem by doubling the healing and doubling the mana cost. It'd be a lot less spammable if it cost 2x as much mana, but if it healed for twice as much (or 1.5x, or something 'balanced'), we wouldn't *need* to spam it as much. The biggest issue with the nerf is that they're basically saying "bad priest, you can't use CoH that much ... but no, we're not really giving you a new alternative, or giving you any reason you *should* cast something else, just nerfing it and leaving it at that".

Fix Renew and nerf CoH in the same patch, and then we're talking. Fix Divine Hymn and nerf CoH in the same patch, and then we're talking. Change Divine Providence to something more useful and nerf CoH in the same patch, and then we're talking. <insert your favourite example here>

Basically, it's a hamhanded way to fix a problem that we all admit existed, but disagreed as to the severity of. Yes, priests were topping the meters. So what? Paladins are coming very close, and they just got a huge buff with the "HL splash" radius going up to 20 yards; and they are still infinite-mana-spam-bots. Rather than nerfing priests, they should have just buffed shamans and to a lesser extent, druids. If you want to make CoH less attractive, provide alternatives that do the same (or a better) job, don't nerf the spell and expect things to magically improve. If we end up with a 7-second WG / 6-second CoH, CHeal becomes more useful for consistent damage (again), and we return to the land of Twin Eredars, where stacking resto shamans made the fight trivial. Either they're going to have to design fights around this (i.e. no more heavy raid-stacked RSTS damage ever again), or in 6 months they're going to have to buff druids/priests or nerf shamans ... again. Not very intelligent design, basically.

Trouble, I think they should have put an 'arcane blast' like debuff on the priest where each subsequent CoH had a certain type of effect:

1. Higher Mana Cost - First CoH is 100% cost, second is 150 or 200%, third is 200% or 300% or however high you want to scale it.
2. Less Healing done - First CoH is 100%, second is 75%, third is 50%, fourth is 25%, fifth is 0% (or you could go 100%, 67%, 33%, 0%)

The cooldown was just a poor idea, and I think will only present future problems

[edit] Reduce Divine Hymn to a 30 second cooldown (or a minute) and oh yeah, now we're talking.

That's actually a really cool idea. I hadn't thought of it, but it makes a lot of sense and adds a good deal of strategy to using CoH. I'm definitely not a fan of a straight cooldown and agree with Nidaba that it's hamfisted. This idea is very elegant in that it limits the spam of CoH while adding tactical decisions to its usage.

Somehow the double mana and double healing makes all the sense in the world to me. Why bother with a mechanic change? Just change the cost of the spell!