Hi Ray.
I’m new to the world of CNC routers. Last year I built a 1000mm x 600mm machine that’s heavy enough to cut aluminium. I use Nima 34 & 23 motors. I found the drive voltage an important factor in providing good torque. Another factor is the maximum cutting speed. Most steppers produce about half of their static torque at 500rpm. So the ball screw pitch is an important consideration which leads on to microstepping.
Another factor is microstepping, this has an adverse effect on motor torque but reduces vibration.
On my machine with 5mm pitch ball screws I used a Nema 23 for the Z axis whilst the gantry axis motor is a Nema 34 and two Nema 23 motors running the table axis. This gives a max speed of 2500mm / min.