RC100 was the original incarnation of the frame, it was sold as a full bike. This was about 1990-91 ish. A few RC100 frames may have been supplied as frame only.
RC200 was the RC100 but sold as a bare frame. Original RC200s are rare as hen's teeth, I'm guessing a lot have been rebuilt/resprayed/rebadged as Rc100s. Pace then stopped selling complete bikes and started selling frame only; this coincided wuth a tweak which was the f2. Original RC200s retrospectively became f1s. So as you can guess the 'f' referred to the next incarnation of the frame which has had a minor tweak of frame. For example, if memory serves me right they had all square tubing upto f4. From f4 on the seat tube was round. When they got upto f8 (which they stopped making about 2002) they also started making a variant with a carbon seat tube - the RC300. With the exception of the change from square to round seat tube, the tweaks aren't that noticeable. The most obvious distinction between f numbers is the decals, headbadge and frame colours.
Pace changed their frame numbers after a wee while (F4) and the frame number tells you which variant they are, this is followed by the size and then the build number. If you look at the Pace Serial number thread ( viewtopic.php?f=1&t=20895
) on here you'll see how it all works, and get a rough idea of how many they made in the 12 or so years square Pace frames were in production. Have a look for Rich's Pace timeline, and the variants are all illustrated.
My RC200f8 was one of the last built, and has an RC300 headtube, which normal f8s don't have. Does that make it an f8.5 or f9?
Why do I ride a Pace - it's all that bl**dy sheep's fault