I currently use a 16t:40t pulley combination with a 1.2Nm motor.

The 5:2 reduction gave me a convenient 200 half steps/mm.

The gutsier motor should allow me a 5:4 reduction thus halving the motor speed and keeping me in the motor torque band, hopefully.

The screws have just under 10um backlash so a 10um half step may be the way to go, approx 0.0004".

I could go for a whacky step resolution, all the software does is take the required X, Y, Z in millimeters, multiply by steps per mm, round it to an integer and off it goes. Any value for steps/mm is okay, I just change the SPM variable, recompile it and everything sorts itself out. The only thing I would lose is convenient cogging on the handle dials.

I cut the cheeks for the Z axis yesterday and it came out oversize, everything bent under the tool side pressure when I removed the last 0.5mm on the finishing pass. I got +35um in the X and +55um in the Y, give or take 10um. Probably would have got a lot better if I'd repeated the pass. This is so much better than before I changed screws, it used to be that within 200um was a good day