Richard,

I could be way off-base here, but I believe that you should be concerned with current handling capability. I'm new to to tanks and electric heli's, so I could be all wet. you can use an 11.1 volt ESC with a 12 Volt supply, if your current draw is, say, 2/3 of the ESC rating without worry of overheating. Ask BIGMIG, I think he has some experience with power issues.

My 2-bits, hope to be of some help.
Splat