When it comes to nema23 motors the AutoTech 570/oz/in 5A steppers are the ones to get.
Fed with 60Vdc of power afaic they're the best out there in the 400+ torque range.

I've tried various kits on my mills and there is always something in there that is lacking.
All the motors on my PM25 (23's & 34) and the controller board have been changed for something better with the psu's and drivers from a 34 kit.

I'll prefer to go seperates from now on.