Good point about PPR and spindle speed. I have a 1000PPR encoder on my big mill that runs up to 7500rpm. That's OK with the Centroid Acorn on that machine but it's possible other controllers wouldn't be so happy with such a pulse rate.

Note that some controllers have a minimum PPR. For Centroid it's actually quite high (1000PPR min, 2000-4000 recommended). In contrast, IIRC, LinuxCNC can manage rigid tapping with just 1 pulse per rev but that's unusual. Worth checking either way.