The slow down I am at right now, is I hit the foward key, nothing happens, so I hold it down for a couple of seconds, then a couple of seconds I have moved like 300 feet. Maybe I got a rotten card, or maybe the a single processor is the problem. Seems like people on PB get better FPS then me.
This particular weirdness happened to me in the Undercity, but nowhere else. Often, my main character's model would get "stuck" in the running pose -- standing stock still. I found that switching to another party member tended to reset this annoying behaviour.
I bulled on through that one level, and everything has been smooth sailing since. So don't despair, Radeon 9000 users! Perhaps, rather than being poor performance exactly, this is bugginess in the software renderer. I could overcome it w/o too much trouble; I hope you folks can, too.
I left my heart in Port Montyhaul.