12 cells would be pusing it with the 5700. 3S lipo has less voltage than 12 nimh cells. In fact, 12 cells is closer to 4S lipo than it is to 3S. As I said, I'd run the 4600 motor.

I know that there are a lot of Traxxas fans on this forum, but I am not one of them, so I don't know if beefing up the drive train on the Rustler is enough for it to withstand what you are going to put it through. I'm only saying that I wouldn't recommend doing what you are talking about doing; but if I were to do it just for the heck of it, I would do it with the 4600 motor. You're gonna need low rpms and high torque. The only reason that I am suggesting trying it, is because the Rustler is relatively light.