You might wanna spec arcane sublety on 2 of your mages so you can spread out the damage, when doing big pulls in later levels some damage can be unhealable, especially if your priest gets kicked while casting. Later on when you get Arcane Power you can rotate the cooldown with round robin macro and have one mage tanking for every pull instead of wasting your cooldown for one pack and killing next 2-3 packs slower ( I use 2 AP per cooldown so it is effectively 1.5min cooldown). Personally I did not spec into sublety to reduce the risk of my priest pulling aggro on boss fights