[AdamHeard]

All things being equal (wheels, etc...) a low gear at 6 fps versus 10 fps will perform substantially better.

It's torque required (at the motor) is lower, so there is less current draw (and voltage drop), and you're operating at a higher percent of free speed. You could push all match long, and at an appreciable percent of your free speed. A faster drive will not be able to push in the same manner, or with much speed as you're very near stall on the motors.

I have not recently done these calculations, but have many times in the past. The above is a generalization, but the trend I convey is correct. The specific numbers and crossover points could be different though.