PCI 2.0 vs 3.0 for SLI setup

I currently have an asus sabretooth 990fx. I also an SLI setup with 770's. I'm told that I would see a drastic boost in performance if I were to get an MBO that supports pci 3.0. Is this true? And by how much? Thank you?

No. Most likely you won't see any noticeable improvement by using PCI 3.0. Right now very few graphics cards can even take advantage of the entire 16x PCIe 2.0 lane (Or so I have been told) so 3.0 is pretty much useless.

It has been shown that you can even run two cards at 8x with PCIe 2.0 with no ill effects. 

http://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/

This link should give you the information you need.

Thank you both. Very helpful article.