I don't understand this. So I underclock the card to around 270 on the memory, and in nascar racing 2003 get 25fps at the start. I up it to around 470 memory, and get the same fps.
That's because your computer probably hasnt had a hard drive format in over a year, you probably have a tone of spyware eating up your CPU cycles, and you're probably not testing the performance of your hardware correctly.
...and on top of that, you probably have a crappy R430 GTO to worsen your problems by a large margin.