heres link..about 1%:
https://www.techpowerup.com/reviews/AMD/R9_Fury_X_PCI-Express_Scaling/18.html
Yes, its beneficial. Scaling is from say 50-80% when working properly. It dkesnt always work properly.
Oh man, thank you very much for that link. The data presented definitely tells the full story. Not only was I surprised by the meager 1% loss when dropping from x16 to x8, I was blown away to see that dropping from PCIe x16 3.0 to PCIe x16 2.0 only dropped performance by 1% as well. For some reason, I expected the difference to be huge.
x16 --> x8 = 1% loss in performance
pci 3.0 --> pci 2.0 = 1% loss in performance.
I also found this very informative video explaining PCI slots:
Basically he explains that pci "lanes" are basically just bandwidth and different CPUs have different numbers of lanes. Most current generations of chips have 16 lanes, 28 lanes, or 40 lanes. Obviously if you're building a pc with 4-way-SLI or any type of setup that requires a lot of PCI connectivity, it's very important to have a processor that has enough lanes (bandwidth) to feed everything, otherwise you're just going to get bottlenecked.
Personally, I wasn't sure if I wanted to go with an i7-6700k, or an i7-6800k. They're similar in benchmarks. One has 2 more cores, but the other has a 25% faster clock speed - so they kind of balance out. The real kicker is: the 6700 only has 16 PCI lanes while the 6800 has 28.
http://ark.intel.com/products/88195/Intel-Core-i7-6700K-Processor-8M-Cache-up-to-4_20-GHz
Obviously having 16 pci lanes is fine if you're only running 1x graphics card. You get the maximum x16 speed. Even if you're running dual SLI, you're only losing 1% per card (according to the benchmarks Earthdog posted). No problem, but if you're running triple SLI, you're going to be downgrading your PCI speeds to 1x8+2x4 take a hit of roughly 5% per card on the slower slots. I'm not sure if that would result in a cumulative effect of 5% + 5% + 1% = 11% or just a total of 5% loss in performance. And then obviously if you want to go quad-SLI, you'd have to get a different chip, because according to intel, the 6700k doesn't support it.
These are all very interesting things for anyone pondering an SLI build to consider.
I have another question. Do M.2 slots draw from PCI lanes as well? I know the old, lower speed slots were connected to SATA ports somehow, but I'm under the impression that the new M.2 ultra x4 slots draw from PCI bandwidth. Can anyone confirm or explain this?
