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Most of us would be more than happy to have just one high performance graphics card in our system. But some power-hungry individuals just need to have it all. When enthusiasts are looking to maximize their performance and crush every benchmark they come across, multiple graphics cards are usually one of the first build requirements that come to mind. Unfortunately, when you’re spending $1400 or more on just your graphics cards, it’s easy to forget the importance of your other components.
For a large majority of PC gamers, a single GPU and a high performance Skylake CPU like the Intel® Core™ i5-6600K or the Intel® Core™ i7-6700K would be more than sufficient to handle modern games. It’s actually much more common for game performance to be bottlenecked by the graphics card rather than the CPU. We’ve seen a lot of people neglect their CPU and motherboard choice in multi-GPU builds because of this. In order to maximize the potential of those multiple GTX 1070s or 1080s, you have to make sure each graphics card is given the appropriate amount of PCI Express (PCIe) bandwidth to shine.
PCIe refers to the interface that allows you to expand your PC with additional components be it wireless cards, sound cards or the most commonly used discrete graphics cards. In the past, motherboards had to use two different kinds of slots which were AGP for graphics cards and PCI for everything else. Nowadays we have PCIe slots in various speeds to support all forms of expansion. The fastest and most important slot when it comes to graphics cards is the PCIe 16x slot.
While a large number of Z170 motherboards actually come with 2 or more PCIe 16x slots for you to place multiple graphics cards in, doing so will actually reduce the allotted bandwidth of each slot. For example, if you place two GTX 1080s into a Z170 build with an Intel® Core™ i5-6600K or an Intel® Core™ i7-6700K, both cards will actually perform at x8 speed rather than a single card performing at x16. Technically, this doesn’t mean the two cards are performing at half speed, it just means they won’t reach their maximum potential. This all comes back to the choice of CPU and an often overlooked specification: “Max # of PCI Express Lanes”.
The maximum number of PCIe lanes refers to the amount of communication channels open for the processor to receive and transmit data to the PCIe slots. For consumer targeted lines like Intel’s Skylake processors which include the i5-6600K, i7-6700K and i3-6300T, the maximum # of PCIe lanes is 16. It isn’t until you look towards Intel’s enthusiast lines like the 6-10 core Broadwell E (LGA2011-3) that you actually see higher PCIe lanes. Although the entry level i7-6800K offers more lanes at 28, we highly recommend the i7-6850K or higher for multi-GPU builds because of their maximum 40 PCIe lanes. Running with a pair of GTX 1080 graphics cards, we’ve seen up to 15-percent gains when using the 40 lane i7-6850K vs the 28 lane i7-6800K.
While most games won’t make great use of the multiple cores and hyper-threading features exclusive to Intel’s i7 series, we can expect DirectX 12 titles to make a huge difference in the future. We’ve already seen a performance increase of 20 percent when using an i7 processor with Hitman’s DX12 mode. With more DirectX 12 titles taking better advantage of multiple cores in both CPUs and GPUs, we couldn’t recommend a high-performance Intel® Core™ i7 processor enough.
If you’re building a system with multiple graphics cards, chances are you are looking to do some 4K gaming and beyond. Streaming, gameplay recording and other multitasking generally comes with the territory, so it’s only fitting to pair your top tier graphics with a top tier processor. The Intel® Core™ i7-6850K will set you back a pretty penny, but it’s only fair considering you are already paying more for each of your GTX 1080s.