I toyed around with frost pve last month and it was utter fail. As a mage we are still mainly restricted to focus firing our targets and as a frost mage the dmg was just not there.
You spend your whole time praying for fingers of frost and brain freeze to proc. You never run out of mana, but since most raid encounters cannot be frozen half of your dmg talents become useless.
Also, its notable to mention i actually casted slower as frost pve then arcane pve. Since you lost the 6% increase to spell haste through Netherwind Presence.
So the end result was small hits, small crits, and comparatively slow spell casting.