First you would have to get into a PCI-Express not AGP model board to run one of the newer cards like the Radeon X1300 Pro and above. And above the model there would be what you would probably be looking for. The OCers around here would have a better idea on the X1600 and X1800 series cards for that.
With ATI and NVidia in a close race the models can be relative in most cases. Half Life 2 ran good on the Radeon 9550 256mb AGP card just replaced along with the old board to now see how it will go with the model now in use. The X1300 Pro doesn't offer the pixel pipelines like other cards however.