nVidia's newest offerings, the NV28's, carry an AGP 8X feature which will offer greater bandwidth to the card. That however, is not all that will change. Granted, a switch from AGP 4X to 8X does offer a 2 to 3 percent increase in speed, but the real news is that by using a 0.15 process nVidia have managed to squeeze more clock speed out of the new cards.
A good example of what the difference will be is the TI 4200, which in its previous form sported a 250 MHz clock but as a TI 4200-8X will carry 275 MHz of clock speed, with some manufacturers possibly aiming even higher than that. This changes the update to the NV25 from a minor upgrade to a faster, but soon to be replaced, standard such as AGP 8X, to a minor overhaul. Much like it did with the switch from Geforce 3 to Geforce 3 TI 500, nVidia chose to increase clock speed as well in order to offer a new product. This, even though the NV30 is set for a possible December 2002 debut.