Honestly, I dunno. I just try to keep an ear to the ground on all things motherboard, and this has been an issue that's popping more often now, and I have no idea why. Not just here on TPU, either.
I mean, we can generally say, that if IVB is used, no matter the board, PCIe 3.0 is possible, link width is questionable though, and dependant on switches used. No problem there, of course, very straight forward.
Using PLX PEX8747, on PCIe 2.0, giving PCIe 3.0, does add some boost to multi-GPU, even though to the CPU is still just PCIe 2.0. So this ASUS board, to me, makes sense for multi GPU users.
Those PCIe 3.0 cards on this board, they'll show up as PCIe 3.0, I am almost willing to bet.
Are they really running 3.0? I guess the PLX PEX8747 makes this possible...or does it?
products like this one don't make this any easier.