what ever it takes to keep it going,I built my mo6 pro with spare parts I had laying around. A random HiTech servo, a Traxxas xlv ESC, pair up with a Reedy 30k rpm motor mad for a wild ride. When I upgraded every thing in my tc4, I put the Novak gtb esc, and the Tekin red line 21.5 motor in it....granted it is not "stupid fast" but it is fun car to turn some laps in
in short, have fun and don't brake your bank account in doing so.