There's already a thread:
[Mage] The Elementalist
Also some discussion here:
Mage PvP Thread (or: Ice Block, discuss)
Your build looks pretty solid. I would pick up imp cone of cold and master of elements though.
Drully hit the nail on the head - this build shines in battlegrounds and 2's and 3's. For 5's Arcane/Frost is still uncontested.