OK, I bit the bullet and installed them. It's fast enough over cable that the 15MB isn't that big of a deal (the Mandrake ISOs, on the other hand...)
Anyway, the install wasn't too bad. Refresh Force worked (note to everyone having problems: it reinstalled my monitor, so I have TWO possible settings in the program. I tried to use the first one, but it didn't work. Once I went to the second one, it worked). 3DMark2K1SE was about the same (50 points off, within the margin of error). I got about a 20% increase on UT2003's botmatch. Flyby was about the same. JK2 dropped a few FPS (about 10%, actually), so something might be afoot with my OpenGL settings.
For those with control panel problems: did you completely uninstall the old stuff? And did you remove all tweak programs (or at least turn them off) before installing? I had to get rid of Riva Tuner (RC 11.1) because of some odd problems.
All in all, not too bad. I'll stick with 'em only because it's too much work to go back!