Riceline: some corrections.
Firstly the X800 agp is faster because the core(430 off the top of my head?) is native AGP technology and uses a bridge chip to convert to PCI-X. Absolutely nothing to do with the "limitations" of PCI-X. The reverse is also found to be true, native PCI-X cards are faster than the versions using bridge chips to AGP - case in point 6600GT.
Secondly, the 16x and 8x doesn't mean squat, as no card is even coming close to maxing out the bandwidth available on AGP 8x. Nor will any card in the forseeable future.