difference in performance between pcie 16x and 8x

Matt da dude

Honorable
Jul 24, 2013
27
0
10,540
For my new build I am giong to be using a corsair obsidian 350d matx case. A mother board that caught my eye was the g1 sniper m5 from gigabyte. It looks like a very strong board but I saw that it only has one 16x slot and should I want to use sli which I will be doing, the I will have to put one of the cards In this slot. In short how much will this impact performance and if it does could you please recommend a new board.