Well the Nforce 600 series does not support PCIe 2.0, but the 8800GT does. So running at 8x is running at 8x, PCIe 2.0 isnt even part of the equation because the board dosent support it. I used to have an EVGA 680i before I knew nvidia chipsets were bad news, and I remember in the BIOS you could adjust the speed betweeen 4, 8, and 16. Maybe go look for that.