I don't have to worry about a prop doing 40,000 rpm. do the math. I am using a clutch, clutchbell and a spur gear. the spur gear is 43t and the clutch bell wil be 18t. that means the prop will be doing 16744 RPM when the engine is doing 40,000. I will be using a prop that will match the load of my MBX5T truggy. at WOT the engine in the truggy has been doing 39,000.