OvrClkr :
You need to go into the Bios and make sure you have SLI disabled. If it is enabled it will run both slots at x8. If disabled it will run your top slot at x16
hey mate, thanks for your input to this puzzling and as yet unsolved mystery.
i'm running an Asus P6T Deluxe v1, and there are no bios settings directly relating to CrossfireX/SLI. the manual tells me these settings are configured in windows, via the nvidia/ati control panels. i found a setting called 'PCIE Spread Spectrum' which can be disabled in order to overclock PCIe. still no joy with this one i'm afraid. this is frustrating the hell outa me.
cpuz and ati control panel both tell me the max supported link width is 16x, yet my 4670 is only connected at 8x, even though it's in the primary (blue) GPU PCIe slot which, theorectically, should ALWAYS run at 16x. there are no bios options to change the speed of the primary GPU PCIe slot, although PCIe slots 2 (white) and 3 (black) can be configured to run at either 8x/8x or 16x/1x.
i've tried all the other power saving features, both in vista ultimate 64 and bios, to no avail.
on the plus side, ati control panel informs me that although the link width is only 8x (which should be impossible), the link bandwidth is 27.9 Mbps, which i understand to be within normal range.
i have everything fully updated and yes, the card is definately in the primary GPU slot. unfortunately, i don't have another card to test the PCIe slot and i bought this PC second-hand, so no warranty; my research suggests some people have fixed this problem by replacing the card, while others have replaced the board.