I'm running a 4000KV 2-pole motor in that car. It's geared for a top speed of 40mph. Traction is always at a premium on the unswept pavement I drive on, but I'm slowly learning which tires work best for me, so traction is slowly improving.

Generally I go with metal gears whenever possible, but since Tamiya is apparently much better at making things out of plastic than a lot of RC companies are, I find myself tempted to see whether the plastic gears can handle the load. But since this is a custom conversion, getting into the gearboxes to perform repairs is more of a pain in the ass than usual.

I know, I'm overanalyzing things. That's part of the hobby for me, apparently. There is absolutely no reason I shouldn't go with metal gears except to see if the plastic gears can handle the load, and also to see if having 6g less weight in the rear actually makes a damn bit of difference.

Why do you say the ball diff would be better for traction? I thought their main advantages were light weight and external adjustability for the limited-slip feature. Do they do something else to improve traction that I don't know about?