I don't know what is best for the Losi, but I know it needs to be fairly beefy, as they tend to burn up in losi if not set up just right.. Doesn't need to be a speed servo, but most run them, especially those that run electrics in the winter.. It iwll feel more like and electric the quicker it gets..

I say you need at least 150 oz/in of torque, and .12sec or better..