It depends what you want to do with the car after you put the mamba in it. For a racecar, either one will be way to much power for that chassis, but you can take that as a good or bad thing. I would probably end up with the 5700 on 3s, but the 4600 on 2s would probably make more sense.
If you end up with stupid amounts of power in that thing, you could try using a gyro on the steering servo to make it a little more drivable.