In such a case the question will become: Can the PCI Express 8x offer enough bandwidth for PCIe 16x graphics cards perform at their peak?
The short answer is simply, yes the PCI Express can!
Truth is, having full 16x SLI support has no real performance benefits over an 8x SLI setup, so again this is something gamers are surely not going to miss out on.
A test was done involving the SLI GeForce 8800 GTX graphics cards to the P5N-E SLI and compared it to the Striker Extreme and P5N32-E SLI (another more expensive 680i offering by ASUS) with the same hardware configuration. The results are very interesting as it somewhat equaled the more expensive board.