I know this topic has been beaten to death. I understand the general advantages and disadvantages of both, and I know everyone with experience prefers one or the other for certain applications. My question is very specific.

One of my Tamiya XV-01s is a rear-motor conversion, meaning the motor directly drives the rear gearbox, and there's a belt-drive that sends some power up to the front wheels. Basically the same as the TA06, but with the motor behind the rear axle instead of in front of the rear axle. Functionally speaking the only difference is the weight balance, the drivetrain otherwise works the same.

Currently I'm running a tungsten-carbide ball-diff in the rear, but after just a few runs I'm starting to notice some roughness in the ball-diff when I rotate the rear wheels by hand. Since this particular chassis configuration forces the rear wheels to do most of the work of moving the car, *and* there's no "give" in the driveline between the motor and rear diff (whereas with most belt-driven cars there's at least a tiny amount of stretch in the rear drive belt) I'm wondering if maybe I should use a gear diff in the rear instead.

Are there any flaws in my logic? Is there some reason I should I keep the ball diff in the rear anyway? Also, are Tamiya's plastic diff gears good enough, or should I spend the extra money to get metal diff gears?