The thing is, without a machine attached, you can't have a proper go at motor tuning - which depends on your motors on your machine, not on Mach 3.
I have Mach installed on two computers - one in my "office" - front room - where I do all my programming and GCode work, and the other in the workshop.
The one in the workshop attached to my lathe/mill is tuned to that - i.e. rapids 40 ipm acceleration at 3. This is the fastest my machine will move reliably - because it is reliability that you must aim for when machining.
The one in my office, I have the rapids set at 160 ins per minute (my lathe bed is only 20 inches long) - four times faster, so that when I am running a test program, it speeds things up a bit, when I am watching. A G1 move does not matter, because the speed for this is specified in the GCode anyway.
The only way to reliably set the motor tuning is to attach the machine. If you ony have the one computer, keep the machine attached, but do not put any tools in so nothing gets damaged.