My thoughts on the crank also. Cantilever cranks aren't the strongest link in these engines. I've said it before and will repeat it here, if I were going for speed, I'd work around a piston ported engine with a dual counterweight crank .. such as a Zenoah or any number of chainsaw engines. Reed valve engines as used for model applications are really mid range, torque producers and don't like to turn much over 8000 for extended periods of time. Any of the high quality piston ported engines will be happy all day long at 10,000 or more. This and the piston ported engines breath their best at high speeds where the reed valve engines become restricted. Using any practical prop size, you wouldn't be turning a gasser at 10K, but propped for 8.5 to 9K on the ground it will easily be turning 10K in the air.