The x300/x600 both use a newer variant of the chips used on the Radeon 9600 line. With the x300, it is basicially a PCI-e version of the Radeon 9550, an oddly slower card released by ATI recently.

It seems in the video card arena, $200 is still around the price point you need to pay to be able to play the more modern games. The PCIe cards that fit that range would be the NVidia 6600 GT or the Radeon x700. Benchmarks ont hese cards against the other PCIe boards is here. It seems very few sites even looked at the x300 much.