[RotarySMP]

I have no experience with Mach 2 (but have only heard good reviews).

I have been a beta tester for TurboCNC and am very impressed by it. For TurboCNC, there is no requirement for both axis to have the same lead (I have 3mm lead on X and 4 on Z).

TurboCNC uses a 1/rev spindle encoder for threading and needs about three thread's distance to get well sync'd before running onto the work. This can be an issue with smaller threads on a long shaft supported by the live center.

During the cut you can hear it altering Z speed to keep sync'd to the changing spindle speed. You want a reasonably fast Z axis, with plenty of acceleration.

Realistically, both controllers are step and direction, so the hardware is the same. TurboCNC is shareware, and cost nothing to try for as long as you want (the developers desere the $60 registration fee). If you don't like it or DOS, then you can change to Mach2 with no loss.