G'day,
I use Mach3 Version 043.056 on my lathe and mill, as recommended by that great sage, Hood. All versions past 043.030 have worked for me. Version 043.030 is the point at which my problem with M3 Spindle speed commands were corrected.
I use a USB Smoothstepper on the lathe, but parallel port control on the mill. The Smoothstepper Plugin that works satisfactorily for me is "BETA2_v015meg". I tried some later versions of the Plugin but had problems with Spindle RPM readout on Mach3 Turn (it would always read zero RPM). So I went back to the version that worked for me.
CSS has always worked for me. I use PWM output for the spindle fed through a PWM to DC Voltage Converter described in my dissertation on my CNC lathe. The DC voltage is then used to control the VFD driving the 3 Phase 1HP spindle motor. I have limited the spindle speed to a maximum of 1100RPM with VFD settings and this is the maximum speed you see in the videos. I set this limit is mainly because spindle bearings start to get hot if I push it too hard. Also, the VFD also starts to complain and issues warnings if I go past 1100 RPM (approx 3300 RPM motor speed).
Regards
Chrisjh