[Takedown]

A mm on a 4s setup with a fan and an external ubec with feigao 540xl on 4s will have plenty of torque and with around 1900kv to 2080kv aka 9xl or 8xl with proper gearing will hit 40mph. Specific combos such as the one ben mentioned arent your only option when it comes to brushless. You should also take a look into the 80a hw esc that mikes selling here on rcm. That would be a great budget esc.