I'm definitely going to follow your build. Looks very interesting. I've got a CNC engraver that I built myself and now building a printer. I spend alot of time researching stepper motors when I was building my engraver. The NEMA 17's that I used are 60mm long. They were the most powerful ones I could find. The are 92 oz-in. (0.65Nm) holding torque, and I must say they are very powerful. I run them off A4988 stepper drivers with 24v PSU. Once the current limiter is set right in full step mode I cannot stop the shaft turning by hand. For engraving they are plenty powerful enough. I can engrave wood and aluminum.

3D printing had ALOT LESS resistance in its moving axis as there is no cutting taking place, the extruder is simply laying down molten plastic. I don't see you having a problem with the NEMA 17's provided they are a bit more powerful than the standard ones. A big thing to consider is your linear rails and how much friction that have. If you are using linear bearings then you definitely will NOT have a problem with 17's. I used drawer sildes for my linear rails and they have MUCH more resistance then linear bearings, but the 17's I have don't slip or skip any steps, even when running at 1000 mm/min.

There are many factors to consider, but remember if you use 23's then you will have to limit the current anyway, and when you limit the current you will limit the torque, so in a way you defeating the object of using the bigger motor.

Let us know what you decide to do.