Why are those motors your only choice? Thy hobbywing motor you have is more powerful than either of those motors. But for sake of answering your question, the 4000kv will be more in line with what you will want to run on 2S. So go with that one if that is your only choice. Alternately if you are allowed, the Tekin 4600 is probably even better if you plan to run on larger tracks.