You could go with the 1500kv 1527, but I wouldn't recommend it. These motors just pull too much current. A higher volt 12S ESC would be fun to try. As for power differences, I think the 1527 is just too strong for a Savage. The parts aren't made to handle it. Even the 1521 is probably too much, but a careful throttle finger works wonders. The 1521 will flip it right on its lid every time, even with the wheelie bar attached. If you want to beat the nitro guys, I would suggest a 1515. It will easily pull past the nitro and be controllable and reliable enough.
To sum it up, 1521 for hard core basher. Racing and higher speed runs against nitro-1515. The 1527-crazy but not really drivable.