ok pcix 1x has the same speed as standard pci, and pcix 16 is 16 times faster than standard pci same with agp, 4x would be 4x faster than pci, and 8x would be 8x faster than pci.
EDIT: y dont you just get a c2d mobo, with sli, and a few pci slots, and get a good pci card. i got this card
and its great, cheap, and has enough power to play some decent games on low settings(has enough power to compare to a 5500 on stock, or a 6200 when oc'ed, which mine is)
setting gpu mem
stock 275 400
oc 390 493
thats as far as i can get, or ittl start getting all weird on me