Figure 6.12 of this document shows that the unit horsepower of 7075-T6 aluminum is minimized (to 0.2 HP/cuin/min) with a 2 flute 1 inch diameter endmill at 5000 SFM (19098 RPM). A 1/4 inch endmill would need to spin at 76,394 RPM to achieve that 5000 SFM. That’s likely why these folks and these folks are making high speed air spindles for milling machines.
Cutting power is proportional to cutter speed and torque, and cutting forces are proportional to cutter torque. So, not only does increasing speed improve efficiency, it reduces machine forces.