Castle Creations motor and ESC combo recommendations for the Arrma Outcast 4s (1/10th scale).

Monster 2 w/1515-2200kv - 15 pinion/57 spur on 4s = ~60MPH
Monster X w/1515-2200kv - 12 pinion/57 spur on 6s = ~70MPH

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.