Several questions

[lincpimp]

Not sure how well it would run, but the 7xl on 3s would be your best choice for heat disipation. You are running about 30mph on 3s with the 5700. If you want to keep the same speed, I am sure it would be ok. With 8000mah worth of batteries you would have enoght capacity too. The L can motor would probably work too, the 9l works well on 3s. The xl can will run cooler for longer than the l can, but both will heat up eventually. The 9l on 3s will need 66/20 gearing to be as fast as you have right now. The 7xl would need 66/23 to match that. I have had good success with the L cans and the xl. I think someone else here runs a 7xl on 3s so maybe they will chime in.