firefox-pgo-beta 3.1b2-1 in the AUR: http://aur.archlinux.org/packages.php?ID=22919 is about the fastest browser I've used yet. (with flash 10.0.d21.1-1 / jre_beta 6u12_b03-1 working perfectly)
I just went through a week of trying a bunch of different browsers. I built midori-git (with libwebkit-git) as well as epiphany-webkit (also using libwebkit-git).... both were very fast but lacked a working jre plugin..... plus there were other things that were buggy or just broke (like epipnany's url search engine).
I also was using google chrome and opera on my Vista partition. They all felt faster than my FF3.0.5-2 that was optimized for my processor (which is still faster than my Vista FF3.0.5.... but this FF3.1b2-1-PGO is feeling much faster..... and pretty stable too.....