Bill,
The Z axis is a servo motor, Kollomorgen, with about 3 to 1 reduction driving a 3tpi ballscrew. The X axis is a 1125oz/in nema 34 with a 2/1 ratio, driving a 5tpi ballscrew. I was a little worried about the reduction on the servo but it drives it just fine, great resolution and speed much faster than I would allow. The X axis has good resolution also, not as fine as the servo, but very good, I use a 1/8 microstepping controller.
The speed of the stepper is not nearly as fast as the servo but more than fast enough for good rapids.
Arnie