Easy question. Set up: 12020/8XL, 14 cells, Strobe Slipper, stock diffs. The 8XL is having problems (the controller is has been serviced and is fine), so I need to replace the motor. Mike is out of 8 XL, but has the 9XL. Is there a significant difference between the two or should I wait until the 8XL is in stock? Thanks!