Hello,
New member here. I just bought the x79 VB10, which the manufacture says, has 2 x PCI-e x16, 2 x PCI-e x8.
I also thought x8/x8/x8/x8 should be possible.
I tried manual PCIE configurations in the BIOS, however, only black lanes are keep working at x16.
Have you tried configuring it too...