I would not have any doubts about this problems you.ve menitioned if there would be a constant. Like, ok 60V is not enough. It should not work. But it varies. Sometimes works just fine.
Changing the microsteps was just an experiment to see if the steppers would sound different. I did adjust the STEPS PER each time I.ve played with the microsteps.

You are right about Nema23, but who knew. I bought this kit more than 3 years ago. And the rails a couple of years ago, and finaly the steel a few months ago. I did some research back then, and I think I did like any guy who did not have experience with cncs. Bigger is better. And it was a whole kit for sale.

I have the hardware available to go with dual ballscrew for the y axis, and then I.ll build some belt system to drive these with one stepper, and here include some gearing to make it faster, and I would do it, if this design did fail. I don.t have any problem with improving or modifing the project, IF there is a clear, specific and permanent error.
All this voltage, microsteps, heavy gantry, direct coupling, mach3 settings would create permanent errors.. It will just not work, or work bad constantly. Is this not true? There is a variable which gives me a hard time. What is it? Who knows.