Can you confirm that Spell Deflection works on AoE abilities like breaths now? Previous testing had led me to believe that it only works if the spell is cast directly at you (ie, KT's Frostbolt). Things that hit multiple targets (like breaths) didn't work. But if it DOES work now, I'll be very happy.

We adopted the exact same strat last night with a similar setup. We found it better to use Bloodlust on Tenebron though as things are less hectic, the DPS still adds up as you get to start on Shadron eariler.

We did find though that the fight is not over when Shadron died, we wiped 2-3 times when we got to just Vesperon as the drake tank damage seemed to be significantly higher than when he had two on him. I'm not sure what happened as I couldn't see it but I suspect the drake tank was going to town on Vesperon and getting smacked for all the TT damage every second. Also the increase in physical damage from Sartharion isn't trivial. It is unfortunate we only got to that poitn so late in the raid, going back tonight to kill hopefully.

We didn't bother killing the portal adds after Shadron though, there doesn't seem much point when he spawns them so fast anyway. Maybe we will try that tonight but I doubt it for all the extra trouble it causes.

First, what is your buffed health using your raid composition while under the effect of Power of Vesperon?

Second, do you have any trinkets which can boost your maximum health for a short period of time, ie. [Repelling Charge]?
Third, here is a list of life-saving measures possible (probably non-exhaustive):

Divine Protection: -50% damage taken for 12 seconds without T7 4-pc bonus.
Diving Guardian + Hand of Sacrifice from another Paladin: -30% * -30% (or -51%) damage taken for 12 seconds.
Pain Suppression + Power Word: Shield: -40%(?) damage taken for 8 seconds.
Roar of Sacrifice from a BM Hunter's Tenacity pet + Discipline Priest's PW:S: 30% damage transferred to pet.
Guardian Spirit: Spirit dies for you and heals you for 50% of your maximum HP.
Health Trinket + Mighty Fire Protection Potion + Nightmare Seed + Power Word: Shield (Here, I need some insight on whether Power of Vesperon reduces the health granted by the boosters listed. I assume it does but want to be sure.)

I apologize for any minor errors in tooltip descriptions here. I'll fix this post up once I leave work today.

There is your reason for your drake tank dying. The respawn on portal adds is something between 45 and 60 seconds, I believe, and they die reasonably fast to make portal hopping worthwhile. If you just ignore them, your Vesperon tank will be taking +75% shadow damage from the Vesperon akolyte, your MT will be taking +75% fire damage from the Vesperon akolyte, +50% fire damage from the Shadron akolyte (which wouldn't even be respawning after you kill it) AND considerably more melee damage from Satharion due to the +50% increase in both melee damage and attack speed. In addition to this, your raid will be taking +75% fire damage from meteors and shadow damage from styles (Vesperon akolyte). All of this for 60-75 seconds until Vesperon is down - quite honestly, I don't see how your healers are supposed to keep up. I was healing the Satharion tank yesterday, and if we hadn't killed the akolytes after Shadron we would have beend overwhelmed by the total damage that was going around, that is for sure.

Edited above post to show the non-split version of the kill in wws log.

That's very interesting, and resistance being counted first definitely explains the weird damage amounts it was reducing. Looking back at our Sartharion kill, I had 2 completely unresisted breaths out of 29. I can't be 100% certain I had Fire Resistance Aura active for those though. Since unresisted breaths would still be possible at Mark of the Wild level resistance, it would still fit into the data you've collected. This definitely makes the possibility of using a resistance flask interesting, as you could guarantee at least a 10% resistance on each breath with just that and mark of the wild.

Again with the caveat that this requires confirmation on boss-level mobs, it's expected the minimum possible resist changes at these levels:

104 FR - 10% min, 20% avg
178 FR - 20% min, 30% avg
277 FR - 30% min, 40% avg
415 FR - 40% min, 50% avg

So just a fire resist totem and a +50 FR flask will knock 10% resists off the table, and give you a long-term average resist of 30%. Beyond that, it will take a bit of enchants/gear to go further, but each 10% that is resisted is up to 6k damage avoided in the 25 man, thus worth the loss of quite a bit of stamina in terms of breath survival. Obviously the tradeoff still exists with making sure you don't end up hammered too hard by the melee.

Our guild done some tries on Sartharion 10+3 this week and im still not sure what setup we should aim for. We will use casster group, but im not sure about the number of tanks and healers. We tried it with 2 tanks and 3 healers, didnt go very well (probably because we had crap raid setup). Another day we tried it with 3/3 and havent made any progress at all I´d say. We had some nice control on adds and drakes, but we failed to DPS down Tenebron fast enough. Correct me if I am wrong, but getting Tenebron down before he pops second whelps is essential ?.
I was thinking about going 2/2 for the next time. The DPS gain would be huge, but I´m more worried about twilight torment healing when Shadron is still up. will it be possible for 2 healers - probably Holy Paladin and either druid//priest to outheal the big raid damage and huge breaths on tank ?

If the gear of your group is good enough and you stack buffs properly, you should always manage to kill Tenebron before he can spawn a second set of whelps (without Heroism/Bloodlust). Once Tenebron is dead your tank can reposition Shadron to Vesperons landing spot while dps clears the adds, then pop your Heroism/Bloodlust and kill Shadron. Once Shadron is almost dead one of the caster hybrids (Moonkin/ele Shaman) starts to help out on healing.

So when you actually need it you'll have the 3rd healer. Seems to be one of many advantages of doing this with casters instead of melee.

Yeah, finally after a long time after we did the 25 man version as well, we killed him with:

• DK Tank on Sarth ( 44/11/16, which is imo the perfect sarth tanking spec =p )
• Warrior tank on Adds
• Prot Pally on Blue Drakes
• Holy Priest
• Resto Druid
• Elemental Shaman ( Healing once Vesperons Acolyte comes up )
• Demon/Destro Lock
• Moonkin
• Shadow Priest
• Surv Hunter

We tried quite some time, had some horrible deaths, like pally getting instakilled from the breath and shit, as we used the druid on raid healing...

Eventually we did an attempt without Bloodlust ( we normally use this after we aoe the adds and dps Shadron ), and we managed to get Ahadron down without using Bloodlust, was kind of hectic then as our priest was out of mana, he got a soulstone, went in front of Sartharion, got his by the breath, healed me for 15 more seconds, used his SS, healed more, then 3 adds hitted the druid, but me ( as sarth tank ) taunted 2 while being constnatly on the verge of dying, was very hectic =p.

About rotations:

When Vesperons Acolyte comes up I used:

Anti Magic Shield
Icebound Fortitude
Vampiric Blood + HP Trinket + Seed which put me at 42k health
Anti Magic
Icebound
Raise Dead ( saved my ass there =p )
Then Shadron was dead

What we realiesd was, that the fire elementals have little health, around 25k

So next week we will try this with a melee group consisting of 2 tanks, 2.5 healers and 5.5 DPS. We will instantly nuke the fire ellies when they come up. They die so fast single targetted so it's no problem at all, the DK has 2 taunts and the warrior has another taunt, so healers should be fine.

To sum it up, I really like this fight 10man, it actually is a good challenge, the 25 man version isn't even fun, we burn shadron too fast, and the Twilight Torment debuff is easily outhealable. Whilst the 10 man version is alot different, and the funny thing is, we didn't even use Divine Guardian on 10 man, which we have 2 times on 25 man.

Unfortunately we still haven't managed the 25 man 3D kill. Apart from the usual voidzone/flamewall deaths we still had some issues with the portals. When Vesperon landed we went in portal and killed shadron acolyte followed by vesperon acolyte. The shadron acolyte however was respawning about 5 seconds after we killed it. Is it on fixed timer or 45~ second after he got killed?

You actually answered that question yourself. The spawn of the acolyte seems to occur in intervals. So if the one you killed, instantly re-spawns, just kill it another time and you should have some time from then.

But I would recommend not touching the Shadron acolyte before Shadron is dead.
Pro's and con's have been discussed here before, so I won't repeat them now.