Due to ANSI standards the blade tip speed cannot exceed 19000 FPM which is reduced from the previous 21000 FPS. It is determined that is the safe operating speed to avoid harmonics, and possible cracking and blade failure. Blade speed use to be a bigger issue than what people talk about and shops had meters to measure it. But for the most part blade tip speed is only critical on push mowers where the longer the blade length the slower the engine has to run to avoid exceeding that limit. On riders and such the belt and pulley system limits the speed to safe limits, and the operating speed of the engine is basically fixed around 3600 rpm.