OK,
I will rephrase the issue.
Remember this is PWM control, not pulse frequency via steps, so the motor tuning is not relevant. Proved this by setting all the values for spindle to zero. The relevant control for PWM are in the spindle setup tab:- motor control ( step and dir NOT ticked, PWM freq 1000 and 5% min) and special features ( ticked feedback in sync and Averaging) as you have seen in the XML.
From cold start or from a reset, MDI a S word "n" ( where n= 500-2000, just happens to be limit of tests)
start spindle from screen button or a M3/M4 ( this is slant lathe so turn in reverse)
Spindle rotates at approx. 120-125% above set speed, speed stable at this speed ( if you implement the PID feature then speed will slowly crawl down to setting, but there are other issues with PID control and so are advised to not enable.)
do another S word and Mach 3 reads correctly the speed and spindle revolves at calibrated revs for that speed. ( PWM control is not infinitely variable, integer frequencies, so will work at nearest speed which normally within 20 rpm)
(to clear the other red herring :IF you forget to reset the OV% then you can get jump to max speed, which I clarified and have now instated in my start up sequence.)
I have seen mention of this limitation, but have failed of later to track the thread and/or any fix, other than writing programs that double issue the speed at the start of the programme after spindle live.
Hope now clarified?