[ACademic]

My two cents. Engines sound wonderful above six grand. And many have profiles and a bottom end w/stout drivetrain to survive above that and still generate power up there. But alot of bad $#it can also happen above six grand...it's like climbing Mt. Everest and going above the fourth camp site into the "kill zone." You may summit and come back to brag about it. Then again, you may not. I personally build my motors to survive no higher than 6,500 and if built right they will pull to that all day long and last several cycles.