NVIDIA GeForce GTX 1080 PCI-Express Scaling @ techPowerUp
 

In this article, we investigate how performance of NVIDIA's GeForce GTX 1080 is affected when running on constrained PCI-Express bus widths such as x8 or x4. We also test all PCIe speed settings, 1.1, 2.0, and 3.0. One additional test checks how much performance is lost when using the chipset's PCIe x4 slot.
http://www.techpowerup.com/reviews/N...press_Scaling/