I'm running 5 mages, and currently I'm heading for something like:
http://www.wowhead.com/?talent=oZZVmGcobxomo
You are talking about AoEgrind as frost, and that calls for imp. blizz and Perma Frost. If you can't target all blizzards, then just screw it.
Questing gives alot better XP than grinding unless you find elites and killing is fast.
I like frost for extra survibilty, Ice Barrier ftw! Also, slow and chance of root is awesome.
With all 5 frost bite and shatter, I have a nice high chance of critting etc. and stuff should die in max 2 rounds of frostbolts = 5seconds.