Let's start from basics.
To travel 500mm in 1 min with a TPI of 6, single start, your screw will need to run at 118.08 RPM.
Does this speed make your motors sound like they are blowing up?
Do you have a belt or gear drive to attached to your screw?

If you have a direct drive then your motor RPM is also 118.08.
Assuming that your screw can rotate at 800 RPM before whipping, or vibrations occurs, you can then get 133 IPM or 3386 mm per min.
Your next issue is too see if your stepper motor system can cause your screw to rotate at 800 RPM.
A lower TPI screw will give less resolution while increasing your RPM for the same motor RPM you currently use. Accuracy will involve a number of variables and thus not a simple answer. e.g. screw precsion, backlash, mechanical tolerances in your build, stepper resolution, etc.

What IPM are you looking for?

For comparison, I have a 425 oz-in Keling stepper motor, a G540 and a 48V power supply. My stepper can do over 4000 RPM no-load. So getting your system to run at 800 RPM is well within reason.