I'm guessing the Mamba 5700 relates to 5700kV (which towards the slower end of brushless motors)? Jason suggests a 17t for a 2* Reedy/LRP motor which I believe are 6500kV rating, so I'd start on a 17 or 18t with the Mamba.
OT:- I've just noticed on the Novak site they have/are releasing a 3.5 (10500kV!) brushless motor
