Steppers are not fast on this type of machine when you compare to servos. It will be however fast enough for most, the downside to me of steppers is the low acceleration when compared to servos.
Ok what I had, on the first mill I did, a manual Bridgeport converted to CNC, was 916 ozin steppers geared 2:1, I then got the CNC Bridgeport and used the same steppers but it already had 2.5:1 reduction so I kept that.
Both of these had more than enough torque and rapids achieved were 2500mm/min @ 40mm/s accel or 2200mm/min @ 100mm/s. I settled on the latter as accel is much more important than rapids. If you have servos of the correct size then you can have both for example I can get in excess of 6000mm/min @ 800mm/s acceleration. So steppers are fine for most but doesnt matter what size you will nt get lightning rapids or acceleration.
Hood