I am still learning, just got a dual GTX1080ti setup (New Gaming Rig) online mining for me and after reading up on some of the 6 card GPU rigs, it seems they use everything from PCIe 1x to 16x, is there any difference in the speeds of mining with them. The reason i ask is i have my old gaming rig sitting in the garage right now that has no GPU in it due to it dieing on me (AMD R9 290x), it has a GA-Z77-DS3H motherboard w/ i5 3570k in it just collection dust, the motherboard has 2 x PCI express 3.0, 2 PCI express x16 and 2 PCI express x1....
The speed of the pcie risers is not considered just as it is not considered the length of the pcie port.
If it is x1 or x4 or x8 or x16 it makes no difference at all in mining with x1 to x16 pcie risers.