Just to throw something else into the mix... I contacted Fehlmann (the makers of my mill) and asked them what they used on the modern equivalent of my machine. They now use Omron "Smartstep" servo motors (R88M-G40030h) with a nominal torque of 1.3Nm and a momentary torque of 3.6Nm. 2.6A mains (200v ac) powered driver.

I'm wondering again whether those Leadshine 3ph Nema23 2Nm closed loop steppers wouldn't do the job or is the torque characteristic for a servo very much different to a stepper?