I found that frostfire was a substantial DPS increase on boss fights in instances, and everything else died too fast for it to make much of a difference. I respecced out of it because I find myself questing with just my two mages most often, where frostfire provided me little benefit. I chose to go back to frost because of the fact I spend most of my time out questing just the two of me. Frostfire is definitely the way to go for instances/raids though. And I do miss the two pyro crits to open up that would flatten a normal mob instantly with my two mages. =D Made me feel like a 5-boxing shaman for a second!

Here are my two 78 (almost 79) frost magi:
Anomalee (main)
Anomali