P1 I use 2 banes and 1 ED,(ED cause I have 3 stacks +aetherflow ready to be cast, so I get it on CD and have 3 stacks for P2.
P2, I don't bane. Just cause we can kill knight+soldiers in time without it, so I just fester 2 times and do 1 ED (because I have aetherflow ready at around when 1st soldier is down cause of the use of Aetherflow during 1st phase).
P3 I fester 2 times with RS and then 1 more fester, then at around 20-30% left on dread, I get new stacks, I use 1 of those to fester or ED, depending on how much I have MP.
In P4 I DoT and bane on bugs Shadowflare and then spamm blizzara II (we get all the buggs killed that way)
Then I just spend all 3 stacks on festers (3 on each phase)

The party we have: War, Pld, Whm, Sch, Blm, Mnk, Brd, Smn(me)

But I'm not saying that thats the best way to use stacks, but thats what works with our party. Just go with trial and error, try different things on each try, until you feel like you've found what works for you and your party.