Castle Creations motor and ESC combo recommendations for the Axial Ryft™:

Mamba X w/1415-2400kv - Stock gearing (15/53) on 3s = ~45MPH
Mamba Monster X w/1512-1800kv - Stock gearing (17/53) on 4s = ~55MPH
Mamba Monster X w/1515-2200kv - Stock gearing (17/53) on 4s = ~70MPH

Fitment note: Installation of 1512 and 1515 series motors requires modification to vehicle frame, motor fins, and linkages.

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.