Dusting off my old Ag Engineering hat from ISU, if I remember correctly- tip speed as it would apply to rotary cutting as well as cutter bars sort of hit a wall at a particular speed (something around 280 FPS, don't quote my bad memory) where the cutting edge is moving fast enough that it pushes over the plant rather than cutting it. With the aide of air movement (like in a mower deck) you can cheat this a little, BUT you run right up against material limits of the steel blade and whatever the consumer does with it. OPEI went above ASAE as a matter of consumer safety (non-farm users & users of walk-behind equipment) and put blade tip speed limits and RPM limits in effect.