What bl motor to use with 3s lipos

[TexasSP]

The 5700 will work great on 3s lipo, that is that motor's sweet spot. You should gear around 15/86 and you should be all good. Just remember that if you will be running in tall grass or deep sand to drop the pinion a tooth or two or raise the spur to a 90t. I also recommmend you get the aluminum idler gear as well because the stock plastic one will strip in no time.