Actually 8x cards are not designed for 1.5v, but 0.8 volt. 1.5v slots are intended for the 4x agp 2.0 spec. Most 8x cards are supposed to be backwards compatible with a 4x 1.5v slot, but that doesn't necessarily mean that it will run stable or at all for that matter. If your agp slot is 3.0 compliant it will run 4x or 8x cards.