forget about that. what about the MM5700? what would that do?

The Feigao 6s isn't a great motor, it sucks amps like crazy, especially on 8 cells. The Mamba Max 5700 system has too high of a kv IMO, it's better for lighter 4wd vehicles (like 1/10 4wd buggies and 1/10 4wd cars) and 2wd cars/buggies/trucks.

You seem to be thinking that the higher the RPM/kv the better. That isn't always the best choice. For good efficiency, it's best to keep the motor spinning at about 40,000 RPM max, and for the HPI MT2 it would be best to use a minimum of 8 cells to get there (a lower number of cells won't make it seem all that great).

This is what I'm looking at the OFNA Pirate 10 for....its a shaft drive 4x4.

cool. i think i will start off with the MM4600 on 8 IB4200 cells. but how should i gear it with a 54T spur gear?

A 13t pinion should get you into the 40~45 mph range.

Here's a few threads regarding my MT2 setup that you asked about.

http://www.rc-monster.com/forum/showthread.php?t=2349

http://www.rc-monster.com/forum/showthread.php?t=3337