I am new today to this forum, but in the interest of safety I must respond.
The United States of America Standards Institute, sponsored by the Outdoor Power Equipment Institute recommends for safety the maximum blade tip speed of 19,000 Ft./Min. Which means the tip travels 19,000 feet in 1 minute. Which is going 3.6 miles in 1 minute or about 215 mph in a car.
Blade tip speed is caculated by the blade length and the rpm of the spindle it is mounted to. The spindle rpm for a 16" blade length/diameter would be 4,542 rpm to achieve 19,000 ft/min tip cutting speed. , The same spindle with a 24" blade length/diameter would be 3,023 rpm to achieve the same 19,000 ft/min cutting speed. The larger the blade length, the less spindle rpm needed to accomplish 19,000 ft/min. There are charts online that show what rpm is acceptable for different blade lengths (saves on doing the math).
Blades fatigue while spinning and after cutting for awhile begin to stress crack. If you hit something hard, it accelerates the fatique. You can figure out what force the blade hits the grass (I am not going to do the math here) and if all is working properly the blade see's the grass as a solid object. You then get a clean cut. Speeding the blade tip speed up, can cause the grass to pull and tear especially after the blade dulls a bit>
The lift wings on the blade are designed to lift the lawn at a specified rpm. Speeding up the blade actually causes the blade to lift less (I have seen this also with leaf blowers where people speed up the engine thinking it will blow more, it doesn't, it blows less). The wings also wear out faster at higher speeds. The biggest concern is that a blade will shatter and become a projectile at higher speeds. I have seen blades go right through most mower decks when they explode. I have repaired many decks after this happens. I can only imagine a blade fragment flying across the lawn into something or worse someone.
If in doubt, contact the blade manufacturer for the correct blade tip speed they recommend for that blade.
I don't want to see anyone get hurt or worse...
My 2 cents worth.
C-160 Automatic A hard working horse