Most ESCs are rated for a certain maximum number of cells. Having used 3S (11.1 volt) lithium polymer packs I am sorry I ever bought an ESC that was rated for 8 cells. I will never go back. If you ever intend to try the new battery technologies I would recommend getting an ESC now that is compatable. I would also recommend getting one that can handle at least 3 times the current of your present project. The weight penalty is very small and you will be able to use it with a bigger motor later.