You might get more response posting to the 12th scale thread.
I don't run a cap or a diode or anything like that. As I understand it a diode helps the brakes be more efficient and keeps the brake fet running cooler, I don't use brakes so I have no need for that. I'm told the cap helps to smooth the voltage out to the motor giving more punch. I don;t really buy this, I tried it and it doesn't feel like it makes any difference. Also I think to achieve this you would need a HUGE cap to have an effect. Also I do not want the extra wieght. I run mainly stock and 19T