When intel socket 1155 mbs run two cards in either crossfire or SLi the slots are running at x8 , instead of x16 .
And it makes no detectable difference to performance .
When you go to pci-e 3.0 x16 you double the bandwidth of ...which is technically interesting ..but since current graphics cards are not restricted by half the bandwidth of pci-e 2.0 x16 .......
..its just a meaningless number
and will be till after your processor is obsolete