Easing Into CNC -- Ball Screws?

I'd like to solicit some words of wisdom from the group.

I decided it was time to join the group since I'm considering moving towards
making my RF-31 dual-use. Here's the relevant background: As a consulting
engineer, I've done a lot of automation system design and implementation,
most recently (several years back) as a certified system integrator for
Cimetrix -- awesome software, poor company (IMO). All of my work was in the
area of micron-precision equipment. Anyway, just to keep playing with
computer control, I want to incrementally (cheaply) add CNC to my RF-31.
I've got an industrial PC that I'll be loading LinuxCNC (NIST EMC), and I
can put together the stepper controllers and power supplies, so that's not a
problem. However, even after searching through the message archives, I'm
still wondering if I can "get away" with retaining the stock lead-screws and
nuts for the near term. I understand some of the issues of backlash
(climb-milling and accuracy), but given that I can minimize backlash with
bearing pre-load and a well-adjusted nut (:-o), what else is there to worry
about if using acme screws instead of ball screws? Friction? Would I need
much bigger steppers to offset friction (eating up any savings in lead
screws)? Your advice cheerfully accepted.

Thanks,

Paul R. Hvidston, N6MGN
ACKSYS Engineering
Upland, CA