Prob a bit late for this but i lvled my mage frost all the way up to 70 and stuck with frost as soon as i got some epic gear i went to arcane fire  41*20 somethign like good mana regan and stil lhave the ablity from fire to use pryoblast and with arcane  in there you get a instance cast every 3 min so every 3 min instant pryo blast 8k dmg :) It was hard to use the arance fire spec out side of raids for awhile but once u get use it, it does great. As of going all fire i found ok for pvp but going all fire all it is just more cricts... Arcane/fire More Dmg by far.