I can't advise you on the video cards, but I can tell you that your AMD Athlon 64 X2 3800+ runs at 2Ghz. (or should)
I'm also running an older video card, a Visiontek ATI Radeon X1300 w/512MB PCI-E, and 3GB of PC3200 (400Mhz DDR) RAM. Like you, I don't get blistering frame rates, but it's solid enough to run everything I do...RACE07/GTR Evo (hardest on it), GTR2 (slightly better, but still pushes the limits a bit), GTL (Better, but only at DX8...FPS ranges from mid-40s to mid-70s), rFactor (pretty solid with FPS similar to GTL, but in DX9), and iRacing (Surprisingly, the best performer as FPS goes)
Also, I'm only running 1024x768 resolution, mainly because that's as high as my HDTV will support in VGA mode. (I really need to get the cables for a digital connection to it!

)
When I bought my card several years ago, it cost me about $200, so $90-$110 for the nVidea cards you're looking at seems pretty cheap to me. But, there are members here with INFINITELY more knowledge of video cards than I have, so...Listen to THEM.

Good luck, JC.
