Castle Creations motor and ESC combo recommendations for the Team Associated Rival MT10.

Copperhead 10 w/1412-3200kv - Stock gearing (12/54) on 3s = ~40MPH
Mamba X w/1412-2100kv - 16 pinion/54 spur on 4s = ~45MPH
Mamba X w/1415-2400kv - 16 pinion/54 spur on 4s = ~52MPH

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.