I know this has come up from time to time on the forums but wanted to bring it up again since I have a couple of NEMA 23 steppers and controllers just laying around. The main factor with being able to run the machines faster is cutting power (mix between the steppers and the router/spindle) and the rigidity of the machine. It seems that with the 76 oz-in stepper motors, the machine is limited to about 10-15 mm/s and about a 1-3 mm DOC (highly dependent upon the material). Anything more and you are at risk of losing steps. For a large machine like the LowRider, it would be advantageous to boost up the cutting power if the rigidity allows for it. I imagine the Dewalt 611 has enough cutting power to allow for faster speeds so that leaves the size of the steppers.
I would place NEMA 23s on the X and Dual Y axis. Dual Z Axis will remain NEMA 17 (it seems more than enough power there).
Has anyone started a mod for installing NEMA 23 stepper motors on the LowRider? I have started some initial designs for the plates and am working to fit a NEMA 23. I mainly wanted to see what people think about it and if there has been any work on the subject.