On "conventional" mills aka modern cnc tools, spindle speed is an important consideration.

For those doing mainly alu, 15-24k spindles are sought after.
This is a difficult area in many ways, for 34 kW spindles. 40 Hp.

Basically, the higher the rpm, on modern machines, the higher the mrr and productivity, generally, Alu.
A high-speed spindle at 24.000 rpm can be double the productivity of a 10k spindle.

But is does not double the production or profits/hr of the machine, nor anywhere near it.
Second-level constraints mean a lot of the fast machining value is lost.

High speed spindles like NSK or Nakanishi are commonly employed on high value jobs with modern cnc mills.
They tend to do high value jobs to extreme accuracy, at very low "push" forces.