Now that you've done that, get yourself a UBEC and put 14 cells on that 9XL! The MM ESC will handle it I think you'll be pleased with the power. :027:
Actually, you should use a UBEC anyway because the BEC on the MM is dissipating at least 2-5 watts of power even on 12 cells. That will free the heatsink to cool only the FETs and should help temps.