As per your link, the Intel IGPs are extra slow, so even a plain PCI bus interface is enough to outrun those. If you had a better IGP, such as ATI's Xpress200, the improvement with an add-in card would be only incremental, no matter what the card might be. Plain PCI is just so very slow that all of the various Plain PCI solutions of the past couple of years, with the exception of the 9200/ 9250 Radeons, and the FX 5200 you selected, are all close to the same low level performance.
One of the ratings/ replies on Newegg includes mention of Dx9. But he is in error. Or still is being taken in by nVidia propaganda. The FXes do not have the real Microsoft Direct3D version of the Shader Two functions at all. They have a unique nVidia alternative that is a great deal slower, such that the fastest FX, the 5950, was slower than ATI's 9600 Pro, a Low End card, when running Oblivion. You can get Pixel Shader Three by moving to a more recent generation of Plain PCI, but with such a restrictive bus, you get rather small speed improvements.