Asrock z 87 pro4

Solution
One is x16 and the other is only x4. So, the difference would be x12. laughing

There is only one x16 PCIe slot on the board you are looking at, the z87 pro.

Tradesman1

Legenda in Aeternum
Thank you, love my Hero! Might want to step the mobo up a bit, with 2x 280x your looking at putting them in a mobo w/ 1 PCI-E3 slot and a PCI-E 2 x4 slot if I remember right, with two cards would look at a minimum of prob an Asus Z87-A for the 2 PCI-E3 slots and can run at 8x8