I'm currently running a http://www.newegg.com/Product/Product.aspx?Item=N82E16814162120 which obviously supports pci-e 3.0 at x16 speed.
The problem i'm having is its stuck running at pci-e 3.0 x4 on my top pcie slot, I'm running a p8z77-v pro motherboard and a 3570k ivy bridge every pci-e slot is open.
The odd thing is that it runs full speed at x8 in the second slot, now thinking it was my motherboard i RMA'd it and received a different board from asus and its doing the same thing as my old board, (x4 top slot----x8 second slot) and i can't seem to figure out why. The only bios options i have is to set the generation of PCI-e and there is nothing to control the the actual speed.
I'v tried running default bios settings, reflashed my bios and changed my link state power management to off and still the same result of x4.