Sorry Splat, you shouldn't use a lower voltage ESC on a higher voltage supply. They do have limits where things will burn out, even if the motors aren't plugged in! (capacitors have voltage ratings, the BEC circuit has to dissipate more volts and overheats, ICs get too much voltage, etc).

You may be able to get away with a bit of over-voltage, but it's not a good idea, especially in helis! Stick to the voltage and current ratings.

I will say that I hate the trend of car/truck ESCs rating current handling in "turns". ***?

D.