Fwiw..
If You are working on a fehlmann..
which is a high-value machine - top of the range -
I would definitely recommend ac brushless servos and a csmio controller.

A motion controller provides much smoother pulses, and at much higher step rates, than other options.
But..
All the high-speed stuff is then dependent on the motion controller, and thus their sw/fw/plugin support is critical.
This applies to high accuracy servos, high accuracy homing, high accuracy probing, etc.

Servos, modern, have 5-10k counts/rev.
Thus, at 50 r/sec, = 3000 rpm, = 500 kHz.
Very few systems support this.

A csmio basic does 256 khz.
It might be fine.
And supports 4 axis.

But..
I think it does not support rigid tapping as-is.
Not sure, check with cslabs.
If this rigid/tapping does not matter, that would be Your best solution, today, imo, ime.

If You want a Really Good solution, get a CSMIO-IP-S or IP-A.
I use IP-S on a lathe, industrial, servos, very happy.

If You want a Really Good solution cheap, get a Pokeys Ethernet board.
Low cost, excellent sw, support, hw.
Limited to 125 kHz, mostly wont matter imo, ime, for the speed.
Mach = 125 kHz but I think Mach4 is higher speed.
6 axis.
And *excellent* MPG support.

I would recommend against anything else, especially usb, exception machmotion and other industrial stuff, I have never heard anything negative about.
So those c/would likely also work really well- no personal experience.
A smart read is that I am not mentioning some popular hobby controllers - some that I have. There Is a Reason.