Well I don't know about FX 5500, but my FX 5700 can run every game that I have with high graphic settings, including hl2 and Doom3. (call me crazy if u want, but that's true) It should not cost much, my gues would be under $100. And Radeon 9800pro is a good card too, for it's price. I can't tell anything from 6600GT since I haven't tried it, but from what I hear it's a very good card, and doesn't cost too much.