We have been looking at a high torque, high power robot for our second machine so we have just been through most of this, minus the actuators.

Building your own gearboxes is hard and comparatively expensive to say the Gimsons. 4 of those will give you loads of push and make it nippy but still drivable (with practice; which I haven't got). You could even go for 6 with the robochallenge wheels and that would be a good powerful machine.

The only thing to change about that is that the robochallenge wheels are a little hard and thus slide on the Hardox floor. If you design it in for future development, banebots do 3 different hardnesses (shores) of wheel. Go with the 40 shore 98mm and that will give you more traction, in theory. You could even go 30 Shore but they are very soft and would grain up like F1 tyres after a while. your choice