RE: What Engine to Convert?
I totally agree with Av8tor. I fly a lot of indoor and I see more people with low powered models crash than those with a lot of power available. I design my models so they fly at no more than 3/4 for most of the flight. Just make sure you don't use the extra power in horisontal flight as you could induce flutter if the airspeed becomes too high (looks spectacular though!)
Michael