 So as a follow-up to my recent video where I took two GTX 580s, threw them on the Gigabyte G1 Gorilla motherboard and I tested in dual 16x mode in SLI and dual 8x bandwidth mode in SLI, I am going to be taking an even higher, an even more demanding card, the Radeon HD 6990, and I'm going to be running it in a single card configuration in a 16x slot, an 8x slot, and finally a 4x slot to find out what difference there is in terms of performance. I'll be using the 3DMark 11 Extreme preset. Now please note that the Extreme preset will not show as much of a difference as one of the lower quality presets, such as the entry or performance presets, but what it does give us is a more realistic real-world scenario because most people are not going to be using a 6990 to run Quake 3 at 1024x768. So you're going to be turning up the details, you're going to be turning up the res, so that is the scenario that we will be looking at. Something to bear in mind before I get too far into my testing here is that the top slot at 16 and the second slot at 8x are both running off the PCI Express controller integrated into the Sandy Bridge CPU on this board, which is clocked at 4.7 GHz by the way to eliminate any CPU bottlenecking, or as much as possible. The bottom slot actually runs off of the chipset at 4x speed, so it has an additional disadvantage that is not shared by the top two slots. So just bear that in mind, take the results with a bit of a grain of salt, but I don't have another platform handy where I can show you 16x, 8x, and 4x where they will all be equal. So my 16x result is a score of 3330, so I'll be back with 8x and 4x results shortly. Now this may look like a stupid configuration, I've got my 6990 and a GTX 580 here, but the reason I've installed the GTX 580, which won't affect my benchmark scores in any way, is to force these PCIe lanes to go from 16x to 8x, 8x. So you can see here within GPU-Z, the 6990 reports as running at 16x, and while that may be true, because it's running internal crossfire where each GPU is getting 16x bandwidth from the lane splitter that's on the PCB itself, the actual lane splitter itself is only getting, if we look here at the GTX 580, so you can see that the actual bandwidth to the slot is only 8x because it is correctly split at this time. So my benchmark results are 3312 3D marks, so we have seen a difference in performance between 16x and 8x, so 3312, okay, very small, very small, and I will be back with PCIe 4x results very shortly. So at the end of the day, this video becomes more about how if you internally bottleneck a card, according to the computational resources located on the card, that the amount of PCI Express bandwidth you supply it with is actually going to make very little difference in terms of performance. Now, something to bear in mind too about this particular testing setup today, you can see I had to nudge my motherboard over a little bit to get the 6990 to fit into that bottom slot on my tech station, but so I've got it in the PCIe 4x slot. Now think about it this way. Basically, I've got two GPUs, I have on a 6990, I pretty much have two 6970 GPUs, okay, so bear with me here. So by the comparison I did the other day where I was comparing 16x, 16x, and 8x, 8x SLI, this is basically running it on this motherboard, this card in 16x mode, it's pretty much like running two cards, two high-end single GPUs at 8x, 8x, 4x, 4x in the 8x slot, and then at 2x, 2x in that 4x slot at the very bottom. That's essentially the amount of bandwidth we have available per GPU, and we still see very, very little fluctuation in terms of the overall score. So what I may have to do in the coming next little while is do an updated video about this where I find a slightly less GPU speed bottlenecked benchmark and demonstrate maybe more of a typical or worst-case scenario for how much the PCI Express bandwidth affects single card performance. So thank you for checking out this little episode of Linus Tech Tips. Don't forget to subscribe for more unboxings, reviews, and other computer videos.