I been researching the 2.0 vs 3.0 PCI-E mother boards for the last few weeks. Here is what I learned.

When you use a single card that supports the PCI-E 3.0 (like the 680 GTX) on a 2.0 mother board, you will lose about 1% performance. How ever if you use more than one GTX 680 card (SLI) on a PCI-E 2.0 board, you start to lose a lot more performance, ranging from 25% and even up to 50% performance loss in SLI.