Motor sizing - revisited

Guys,
I've gone into the archives, and read the formulas for motor
sizing, and some of the replies, but I have a further question. My
Enco mill has pretty easy movement on the x-y axes, but I intend to
make the knee the z axis, and the cranking required to raise and
lower the knee requires considerably more torque. Do I use a
different size motor on z, do I do it by gearing, or both. I'm
thinking ahead to a particular project that requires drilling 10
holes through a piece of steel tubing. Can I cycle the z axis quickly
enough to do this in a timely manner? I don't want to use the quill
fine feed as z, because of an excess of backlash. Any suggestions or
experiences that might help my thinking?

Marv Frankel
Los Angeles