Hi...i am a new user here. I think its more like which motor is better suited for the application.In a heavier car, the 1600kv can run safer on 6s, can be geared up, and generate less heat than the 2000kv motor so that's why most would say 6S/1600. But, geared correctly, you can easily get away with running the 2000kv on 6s.