Dunno about theoretical bandwidths but there's a good comparison chart here for the 7970. There's not a lot of difference between PCIe 3.0 x16 and PCIe 3.0 x8 (which is equivalent to PCIe 2.0 x16) but bear in mind that the GTX 690 is about twice as powerful. Have to wait and see when the 690 reviews come out.Out of curiosity what is the difference in PCIe x16 2.0 and GTX 690 bandwidth?