8/4/4 PCIe 3.0 does not mean you can use 2.0 cards as 16/8/8 BTW; you will still have the same number of lanes, just they will run at PCIe 2.0 spec instead. So, assuming the same 2.0 cards, it will be no different than running them on a SNB CPU. Yeah the 'main' PCIe controller is on the CPU, hence why the older boards often support 3.0, electrically the board doesn't have much to do with it.