Instances ease and FrostFireFollow

There is no doubt that a FrostFire Build has the potential for more damage and that a FrostFire does more damage than a fireball or frostbolt, but I'm finding that fights in instances are so fast that the casting time differential may be an issue. I haven't seen any math on this, but in a short fight it seems like frostbolt with the glyph of frostbolt might do better with a cast time of 2.5 sec along with the having the elemental out.

I am going to setup a fire build for 10 mans and 25s while a ice build will be for 5 mans. I would only need to swap out some trinkets and I will be set.