Sorry for not replying...I've been in the car forums as you can tell by my avatar. britbrat, I can swing a prop 10" in diameter or less, if I swing like a 9x6, I can actually cut the engine mount shorter, lowering the CG. I drag raced a brushless RC18T down a empty parking lot the other day, running a 10x6 prop and 10% fuel. I accelerated faster than the 18T, but I topped out just a hair faster. Then, this 30MPH gust blew from behind, and being a air powered car, it swerved into the RC18T, then went head-over-heels, catching an edge on the 18T's body, but it meraciosly flipped over on all fours, and I continued driving. Then, our radios went out of range and the RC18T took off at Wide Open Throttle into a curb, scratching the bumper, and my engine shut off because the failsafe took over. Thanks goodness I had a failsafe!

So ya, theres my day, and I live at ~600 feet above sea level, so I think I'll try swinging a 9x6 later on.

thanks for the replies!

Oh and for noise:
RC18T= Silent
OS .40 = loud, 2 stroke exauhst blowing everywhere.