[suicideneil]

Your motor will run in its maximum efficiency zone with the 2000kv + 4s lipo setup, 1600kv and 4s lipo will be rather slow and need quite tall gearing = heat up the esc and batts possibly.

I would also run the emaxx on 1600kv 70mm motor & 6s lipo, again to keep the motor runnig efficiently and cool. Running it on 2000kv and 6s lipo will need you to gear down alot like you have with 17/12- keep an eye on temperatures of the esc, motor and batteries.

You will likely find that your emaxx transmission gives out before too long, but there are several options to make it more durable, same with the differentials.