Stick with the 1521, I did the 1527 on 6S and it wasn't controllable at anything over half throttle. In fact it wasn't even that fun to drive. I have a 1521 in my Savage now and that is much better. I use the 1577kv with 6S Flightpowers and a gearing of 52/16. Good mix of wheelies and top speed and temps stay reasonable. Get the new high speed 3rd gear set that just came out and top speed is even better! The only drawbacks are you still get a lot of busted drivetrain parts! Guess that goes with the brushless territory.