Well yes, my Sandy Bridge does not support Gen 3
Still why x8 then not x16? GPU in x16 slot.
BTW mobo says gen 3, but depend on CPU in my case 2.0:
The GIGABYTE motherboard is fully configured to provide gamers with the latest Gen.3 PCI Express technology, delivering maximum data bandwidth for forthcoming discrete graphics cards.
* PCIe Gen. 3 is dependent on CPU and expansion card compatibility.