The 4 pole torque is optimum at the base speed, so with a standard motor you can go up to 120hz.
If you are buying new you could spend a bit more and look at the vector rated motors, these generally take you up higher in the rpm max range.
Also suppliers like WEG have motor/VFD combinations that offer 100% torque down to zero rpm with no cooling fan.
A nice features to have on a spindle is up-to-speed, which would need an input into Mach, not sure if it has the option written in.
This way machining motion is delayed until the spindle is up to speed.
Nosmo.