I looked at the Tango motors on towerhobbies and I'm starting to like the specs of them! High operating temperatures, segmented magnets, stainless steel cans, built in fan, and much cheaper than a 22 series (in my mind that is what I compare it to), the torque has to be great, because of the large diameter. The shaft is 5mm and is hardened steel too, which is a nice feature! They claim that the efficiency is 89%, which is really good. I may be looking into these in the near future. :Love:

EDIT: Look like it's only rated to 25,000 RPM! The 640 KV version on 37 volts (10s) would give 23,600 RPMs, but I don't know if that could still give good speed? I'm sure you could gear it really high with all the torque and low amp draws..?