Stepper Torque for a 7x18 Mill Drill (acme screws)?

I"m starting to get my ideas all in one place to retrofit my older Enco Mill/Drill (approx
7x18 travel).

For XY travel on the standard (but well adjusted and very minimal backlash) Acme screws?

Would 400 Oz-In Steppers be adequate? More? Less? More is better.. but I'd hate to
GROSSLY over-motor myself if I don't have to.
I DO plan to eventually upgrade to ball screws.. but one chunk of money at a time.. I'm
POOR! I want to get the controls and motors (which I know least about) done first.

Thanks!

Paul F.

PS Thanks to those that emailed me regarding my last post on control/drivers.. the Gecko
or Stepperworld boards are sounding best.. so far...