I went from a Geforce 3 Ti200 to a Radeon 9500 pro (128 bit). Like bloom said, there wasn't a HUGE performance boost, but enough to keep me happy.
I currently have an AMD 1.2ghz CPU with a K7S5A mobo and 384mb PC2100 ddram. I bought the CPU/mobo combo two years ago and its beginning to show its age. I'm assuming the CPU is holding back the vid card's performance.
Aces High average framerates are in the 50s. 90 by myself and anywhere between 40-60 in action.
I think Pfunk had posted something about a Radeon 9500 non-pro cards that can easily be 'upgraded' to 9700 status through a software tweak. Some have reported a checkerboard effect in some games with this tweak. A hardware review mentioned that ATI simply takes defective 9700s and calls them 9000/9500s without all the fancy doodads. (?) Eh, I guess if you're willing to take the risk, a 9500 non pro card goes for about $140 (?)
I bought my 9500 pro for $200 a few weeks ago at CompUSA including a warranty. In April when the "9900s" come out (
http://www.theinquirer.net/?article=7589), I assume the 9700 price will drop. I think (if it works out) I'll just exchange the current card for a 9700 pro.