You're trying to have a discussion of specific data with conjecture such as "seemed", "guesstimate" and a whole "50+ casts". While your intentions may be well meaning, please either run the simtool and come back with SPECIFIC data or stop.
Last I tested on Live of 50+ casts, Fireball seemed to do more than Frostfire Bolt - and this is what I based my theory on. If the damage is indeed comparable then I retract some of what I said, in that FFB should never be cast except to refresh the duration of the DoT. I would guesstimate that once you reach ~35% crit on your character sheet, FFB would become more viable than FB.