I would say the RCM heatsink since it has more mass and fin area from what I can tell. You could always run both and see which one provides cooler temps. To get maximum benefit, it helps to put a little thermal compound between the heatsink and motor. Just a little though since it will spread out, you don't want too much or it'll squish out and make a mess.
mass wise the novak is bigger and weighs more.. sice it dosent cover the entire motor i was thinking about buying another one and just cutting it to fill in the gap. the rc monster is very nice but i just dont like how small the fins are and how not much airflow gets around them. the novak fins strech up about 1.5 in..
thermal compund.. will the one from radioshack be sufficent? its kinda pricy but if it will benifit greatly its ok.
If you are planning to use it on a Feigao based motor the RCM heat sink is by far the better chioce. It will hold the motor together while adding extra cooling.
The Novak HV heatsink will actually add mass to the motor and probably make the front end bell pop off sooner cuz it will add weight to the motor and force the motor to support more weight when landing jumps.
I can't decide if its more fun
to make it...
or break it...