My current comp is Prot pally, Holy Priest, Destro Lock, Frostfire Mage, Elemental Shaman. My shaman is practically a fresh 80, with mostly PvP gear from my AV power leveling, but still manages to keep up with my geared out lock and mage. Adding the shaman, with totem of wrath, and windfury boosted my lock and mages dps considerably. My mage is dual spec Arcane/Frostfire. Arcane is a mana hog, even with all the regen i have, i have to use evocation and mana gem every cooldown. As Frostfire, I have to manage hotstreak procs, but it's not that bad (comes in handy in direbrew, when it happend to proc right when the mole machine knocked the mage up in the air) As it is now, each of my toons fights for max damage and dps in shorter trash fights, but boss fights, the lock is usually on top, followed bye the mage, with the shaman not too far apart, considering his gear (PvP purples and quest greens)

Heroism is something that makes a lot of "quick dps race" heroic achievements possible. I just wasn't able to down trollgore fast enough before, and first run with the shaman and I got it. Plus, totem of wrath is like a 25% increase to my pallys spellpower, which I'm pretty sure boosts his dps a lot.

I havent tried swapping my mage back to arcane since 3.2.2, ill have to give it a go, but I think the scorch crit debuff is also helping my overall group's dps, and fire is much more mana efficient, at least it was when i first dual specced her.