Which motor would be better in a
 

Kyosho US Sport truggy w/ 4s (for now) the 8xl or 10xl?

8xl, you can run lower gearing for the same top speed. A 1515 1y would be a better (and more expensive) choice.

I got the 1515 1y in the revo I would like to get another one but need to go the cheaper route for now. Just got a 1965 Mustang to play with. The 1515 1y will be coming later along with the MMM. Just looking for the cheaper route now. Only been playing with nitro for a couple months and already tired of it. Thanks again for you help Linc.

8XL, when you say for now, are you meaning the motor and batteries?

Yeah both actually. Only have the MM so 4s is for now until I get the MMM and then a neu later on. Plan on adding a couple of 2s to match up with the 3s I have for 5s (after the MMM).