high frequency spindle motors

Some time back someone mentioned using a VFD to drive a high frequency
spindle motor. I acquired several high frequency spindles but not the drive
generators.

The spindles have the following specs;

2 pole 3 phase
1.2 kW at 40000 RPM
5.5 amps
167 to 667 Hz.

>>50 to 200 VAC<<

I understand most VFDs only go to 400 hz., but that would still get me the
24000 rpm I need. What I don't understand is how the voltage plays a part
in the motor control. Does the voltage have to be changed for different
loads or speeds, or is the rating just a usable range?

-Bob