I've played a 39 Frost mage (tried fire aswell) a LOT. However, I found myself getting oom a lot as fire. If you roll fire you should (imo) ditch Fireball and go Scorch/Fireblast/Blastwave. You can aswell get the 3/3 frostbite which really would help out. As (let's call it) a Scorch Mage you...