The stepper motors I have are Linengineering 4118S-62-07 motors. They were a surplus item, so unfortunately the datasheet doesn't seem to be a very common.
My motors are rated for 2.5A per phase, and a resistance of ~1 ohm is cited in a catalogue with a ~3.6Kg-cm torque.
Looking at http://www.linengineering.com/site/products/4118.html and extrapolating a bit, my motor would be something like the 4118S-04V, or having approx the same torque the 4118S-04P does, just at twice the rpm.
So when I'm running my mill at 2000mm/sec on a 1.25mm pitch, that's about 26 revs/sec. Which would be something like 1600g-cm of torque from my wild guessing and eyeballing the graph. Which, frankly, isn't too bad at all at all!
If I get this ACME at 10tpi (or 2.54mm pitch), I should be able to run a similar speed, but at 13 revs/sec and ~ 2200g-cm of torque. When is very reasonable indeed. Ok, I'm sold.
Now I'm off to buy some 3 meters of ACME threaded rod.