Honestly, I would recommend the 10XL. I have that very motor on a converted Revo and its pretty fast on 14 cells. I would say around 40+ which is more than I need for racing. I run 20/51 but I think 18/51 will provide better runtimes. If you are gonna run 5S I would recommend the 10XL. I was going to get 6S lipo to run on mine but after 14 cells, I don't really need that much power so I'm gonna go for 4S. It would be a little faster than it is now. I think you'll be happy with the 10XL.