A gentleman from Castle Creations told me that the BEC will convert the extra voltage it has to drop into heat (so the 3 cell LiPo will run the ESC hotter than the 2 cell LiPo). Because of this, for their programmable ESC's anyway, they recommend using fewer servos. I'm assuming more servos means more current running through the BEC which means even more heat.

Adequate cooling for the ESC would seem to be in order if using 3C LiPo.

For those in the know, please correct me if the info is incorrect. I contacted FMA about the same thing and they gave a slightly different answer to my question regarding 3C LiPo's and the number of servos that can be used.