So I think I have a few things figured out. I found a handy little stepper motor calculator here: Stepper Motor Calculator
In terms of power the StepperOnline NEMA 34 stepper is capable of about 360 watts at ~200 RPM (assuming 5.0 amps, 11mH, and 72 volts)
In terms of power the Link Motor NEMA 23 stepper is capable of about 216 watts at ~1000 RPM (assuming 3.0 amps, 3.8mH, and 72 volts) or
In terms of power the Link Motor NEMA 23 stepper is capable of about 302 watts at ~675 RPM (assuming 4.2 amps, 3.8mH, and 72 volts)
So that essentially rules out the steppers!
For contrast, I have some horrible Long's NEMA 23 steppers with much higher 6.8mH inductance which I now understand is completely bad for speed and adds nothing to the motor's ability to get the job done. It looks like this:
In terms of power the Long's NEMA 23 stepper is capable of about 216 watts at ~530 RPM (assuming 3.0 amps, 6.8mH, and 72 volts), which I had been running at 36 volts previously, and wondering why they sucked so bad when I pushed them a little.
Well at 36vdc I would be lucky to get 275 RPM out of the Long's 23HS9430B! Where the Link Motor 23H2A2442-01B can run away from it at nearly 475 rpm at 36vdc and the same 108 watts of power.
Naturally, you can get higher RPM's out of these motors than what is listed above, but with no real torque/power. Current by necessity would have to fall off to increase speed, leaving you with a relatively powerful slow speed motor, but nothing on the high end.
I guess I should just not F around and put the Yaskawa servo in place to run the spindle, because at 750w it should have plenty of power everywhere for a mini lathe (8Nm from 0-3000 RPM peak).
I really don't see a need on the little lathe for anything over 2500 RPM and I can gear reduce it from 3000 RPM max to about 1200 RPM max with the spindle head.