I don't see how motors working at their designed voltage on 100mm wheels is pushing it, really... It's only like having 16:1 banebots gearboxes and smaller wheels, same end ratio I mean. Plus we have four, so the load is spread out. If you're referring to Robob, I believe he's using 75mm wheels.

Also the issue with Robob's setup isn't the motors overheating at all, which is our experience with overvolting 12v motors to 5s, it's the torque they produce as a result of overvolting that kills the gearboxes. I'd still be running 12v motors at 18.5 if there were suitable gearboxes that can take the stress. The motors do get warm, but nothing more than I'd expect, and the power you get out of them is awesome.