[lincpimp]

I can say that a 7xl will work fine on 4s. Just gear for about 35mph and check temps. You can gear up as temps allow. With good batteries you can get 45mph out of a 7xl, but 40mph will yeild better temps. Most go to 8xl as they can gear up to make up for lost speed due to a slower turning motor. And motor temps are supposed to be better. I am not sure if it is worth the extra cost.

I have a few 7xl motors and they work fine on 4s, no reason for me to change!