More voltage also means more wear on the motor. Be carefully, certain motors can only handle a certain amount of cells. As a general rule, 540 (also called 05 motors, or standard car motors) really should only be run on 7 cells or less. They can be run on 8, but they won't last long at all. On 7 cells they'll wear a lot faster than on 6 and need to be rebuilt more often.