The upgrade to Gentoo is almost done now. In the middle of things I also gave the new OpenSuSE 10.0 a whirl. Although many things are improved, some things are also broken (that may well be fixed in the 10.1 release). I can't say I'd recommend an upgrade to anyone using 9.3, but it does boot significantly faster now and uses the newer 2.6.13 kernel. My biggest problem was that artsd was all but unusable no matter what I tried. I also had to monkey with some startup scripts to get the radeon and drm working properly.
Anyway, wrt Gentoo, there is a noticable speedup in both cold boot time and running performance. I'm using a 188.8.131.52 vanilla kernel patched with the latest swsusp2. The only problem I'm having right now is that "iwlist ra0 scan" returns "driver does not support scanning" that I need to look into. It works fine and connects to any network but part of my frontend needs the scanning ability. Once that's solved it'll finally be back in the car. It took WAY longer than I expected to make the move but the difference in speed and stability was well worth it.
It will be interesting to see how well swsusp2 works over time. The swsusp used by SuSE (not swsusp2) was very unreliable.