I think it's all down to what they will take, I had the same issues when I built my table with 23's, I have the same Z screw too. That is the same motor I have on my Z axis, on the X & Y axes I have the larger 4A nema 23's, my table is all belt drive apart from the Z which is direct.
My machine is a small plasma(600x600 cut) and found i could put the speed up to silly values which i thought was great until i started cut-testing in and found the weak spots - stability, belts, torch wobble etc.
I had to slow her down a bit but push the acceleration up to get good corners.
I used the auto-setup to fine tune my steps-per figures, it works very well when used across a large distance.