Tank rotation:
I don't remember where, but I saw some math regarding the tank rotation on P3 so I went and reproduced it using Excel.
Estimations:
Mutated Plague: Shadow damage to the raid every 3 sec. Stacks.
Increased expo rate (see below avg. values taken from our WoL)
Avg Values per stack
1 - 300
2 - 700
3 - 1700
4 - 4500
Tested 4 rotations:
1-1-1-2-2-2-3-3-3-4-4-4
2-2-2-4-4-4
2-2-2-3-3-3-4-4-4
4-4-4
Raw data:
Summary data:
Full data for best options:
I believe that it's quite obvious that you want to keep the stack as low as possible => best rotation is 1-1-1-2-2-2-3-3-3-4-4-4 by a small margin over 2-2-2-3-3-3-4-4-4.
The other 2 are more taxing, so 2-2-2-4-4-4 should be ruled out - it puts too much stress on the healers.
After ~100 seconds all rotations even out but as you can see from the last graph - 100 sec is basically the time when lots of people - especially healers - will start dieing, as the damage per 3 sec is ~8K to the whole raid which is simply too much for the healers to handle.
Now, the only thing that we have to worry about is perfecting the taunt rotation to work with 1-1-1-2-2-2-3-3-3-4-4-4
(I'll take an educated guess that the boss is not flagged with the Taunt-resistance flag so we won't be seeing taunt immunity issues).
Another note, we can have the Paly tanks (I don't know if it's viable for healers) spec into Divine Guardian for the added 20% damage reduction and pop it toward the end of the fight - however this is a bit tricky cause that tank will need quick healing to get him back up before he dies to the Plague DoT.