Neither of 9600 GT or HD 4670 are fast enough to utilize PCI-e V2.0's supported bandwidth so no performance increase over PCI-e V1.0 for these cards.
And right now, the cards don't use the full capability of PCIe 1.1 yet, as which single card has 250MB/s bandwidth(leave HD4870 X2 and GTX295).Basically PCIe 3.0 is double the speed of PCIe 2.0 is double the speed of PCIe 1.0.