I went fire all the way. But I had a pocket healer.

Fire = max dmg lower utility / CC.
Which is fine if I can shield and heal.

Frost is a great spec for CC and taking multiple enemies. It lacks some of the strength of fire though (mostly DPS).

If you are 2 boxing, your strategy will likely be more successful going frost than fire - as long as you can control both and individually trigger ice blocks, etc.

That is nearly impossible to micromanage with 4 mages - and higher dps means people die faster, an obvious advantage in PvP.