If I went fire with 3 or more mages, I'd definitely go with a scorch impact spec. Lots of crit, extremely mana efficient, and since you have 3 or more mages you stack the scorch debuff so fast it's like it's always there so the damage is there as well. Also, with impact on that many scorch mages things will spend most of there time stunlocked.

http://www.worldofwarcraft.com/info/classes/mage/talents.html?tal=000000000000000000000000552020103 0303000000000000000000000000000000