I don't have any of the Bit motors (only the stock/upgrade RS Zaps' motors), but I always run the red gears and purple motor. Most of my Zapping is out in the driveway in front of my house, which really has the room to let 'em get up to speed -
Hehe, I *also* like my blue motor/blue gears combo, *perfect* for running around on the coffee table LOL -