Castle Creations motor and ESC combo recommendations for the Redcat Machete 4s:

Mamba X w/1415-2400kv - Stock Gearing (15T Pinion)  on 4s = ~33MPH
Mamba Monster 2 w/1512-2650kv - 16T Pinion on 4s = ~39MPH
Monster X w/1515-2200kv - 16T Pinion on 6s = ~49MPH

Note: All speed estimates are with stock tire diameter, high quality batteries and appropriately sized battery connectors.
Always monitor ESC, motor and battery temperatures on new setups or when changing gearing or batteries.