When it comes to high-performance CPUs, over the past few years there have been a few choices: Intel, Intel, or Intel. Indeed, we haven't recommended an AMD CPU since early 2013, although it's possible AMD's new Zen microarchitecture will deliver on AMD's promise to reset the price-performance curve. In the meantime, gamers looking to maximize performance should be considering only Intel's high-end, overclockable offerings.
But which CPU is best? Intel's enthusiast line starts with the Core i5-6600K quad-core at around $240, and goes all the way up to the Core i7-6950X ten-core at $1,650 or so. When deciding how to allocate a budget for a gaming PC, does it make sense to get the 6600K and pour all the rest of the budget into one or more video cards? Or would a more prudent, long-term perspective be to go for the Core i7-6700K quad-core plus four virtual cores, or perhaps eight real cores with the Core i7-6900K? We've actually asked similar questions in the past, for instance when we published our take on The Best Gaming CPUs: Pentium vs. Core i3 vs. Core i5 vs. Core i7 in 2014, as well as our 2015 showdown between the Core i7-4790K and Core i7-5820K Haswell-based CPUs. In that comparison, we found the two CPUs to be quite evenly matched, with the six-core 5820K surprisingly not pulling ahead in most games. Well, another year has passed, and now we have Skylake-based quad-core CPUs and Broadwell-based six- and eight-core CPUs, so it's time for another shootout!
Given that we previously found that a six-core CPU wasn't any faster than a quad-core, we decided to pull out all the stops and go straight for the eight-core i7-6900K this time around. Given that the Broadwell-E chips currently available on Intel's "Enthusiast" platform actually have a disadvantage in terms of instructions per clock cycle (IPC) versus their more mainstream cousins like the Core i5-6600K and Core i7-6700K, the additional cores may be particularly handy. Right now, Intel's six-, eight-, and ten-core CPUs use the Broadwell-E design, which offers 5-8% lower IPC than Skylake, and also runs at lower default core clocks due to the heat generated by their greater number of cores. Don't worry, we're going to take care of that last minor issue with judicious use of overclocking!
Now, a word on our view of CPU benchmarking. Back when your humble author was a government regulator at the Department of Energy, overseeing standards for a broad array of consumer electronics, we had a term for what happens when the industry asserts a bit too much influence on the regulation-setting process: "agency capture." We think the same thing happens when companies like Intel, Nvidia, and AMD send out engineering samples to eager journalists to perform performance-based testing. For this reason, The Tech Buyer's Guru does not seek, nor will it accept, free samples of CPUs or video cards. Instead, we buy all this gear with the proceeds generated by the site. If you'd like to support additional testing of this nature, feel free to browse our Buyer's Guides and use the links we provide the next time you're ready to buy a new PC product!
With that explanation out of the way, we can move on to the specs for our two test platforms. First our Z170-based system, using Intel's quad-core processors:
- CPU #1: Intel Core i5-6600K
- CPU #2: Intel Core i7-6700K
- Motherboard: Gigabyte GA-Z170X-Gaming 6
- Video Card: EVGA GeForce GTX 1080 Superclocked 8GB
- RAM: Geil 2x8GB Super Luce @ DDR4-3000, 15-15-15-15
- SSD #1: Samsung 850 Evo M.2 500GB
- SSD #2: Crucial MX200 1TB
- Case: Phanteks Enthoo Evolv
- Power Supply: EVGA Supernova 850 GS
- CPU Cooler: Noctua NH-U14S
- Operating System: Windows 10
And second, our X99-based system, using Intel's best eight-core processor:
- CPU: Intel Core i7-6900K
- Motherboard: Asus X99-Pro/USB3.1
- Video Card: EVGA GeForce GTX 1080 Superclocked 8GB
- RAM: G.Skill 4x8GB Ripjaws4 @ DDR4-3200, 16-16-16-36
- SSD #1: Samsung 950 Pro M.2 512GB
- SSD #2: Samsung 850 Evo 1TB
- Case: SilverStone Primera PM01
- Power Supply: EVGA Supernova 1000 PS
- CPU Cooler: Corsair Hydro H100i v2
- Operating System: Windows 10
A few comments on overclocking here. First, the 6700K comes from the factory running at a much higher clock speed (4.0GHz) than the 6600K (3.5GHz) or 6900K (3.2GHz). In practice, the difference isn't quite that large, because under a full load, the 6700K stays at 4GHz (boost to 4.2GHz only occurs on single-threaded workloads), while the 6600K runs at 3.6GHz and the 6900K runs at 3.5GHz fully loaded. We're therefore including these clockspeeds in all of our charts to remind the reader what "stock" really means. But to even out the mismatch as much as possible, we overclocked all three CPUs to 4.4GHz, which is very easy on the 6700K, relatively easy on the 6600K, and near the limit for the 6900K. Even so, as we've already mentioned, the Skylake architecture used by the 6600K/6700K is a bit faster than the 6900K's Broadwell-E design, meaning the quad-cores still have a slight advantage on a per-core basis. Some may argue that an "equal" overclock would have pushed all CPUs to their maximum overclocks, but because this varies widely depending on luck of the draw (also known as the "silicon lottery"), there is no such thing as a universal maximum overclock. We had to draw the line somewhere, so we decided to just run them at the same clocks. Another minor point: because the X99 platform can't run DDR4-3000 memory without an oddball 125MHz motherboard strap, we overclocked our RAM to 3200MHz, 16-16-16-36 on the X99 system to allow it to run at an even 100MHz motherboard strap. The quad-cores ran DDR4-3000, 15-15-15-35, which works out to nearly identical bandwidth.
One other thing that differentiates the hardware: the Core i5-6600K has just four cores to work with, while the Core i7-6700K adds Hyperthreading to give it four "virtual" cores in addition to its physical cores, and the Core i7-6900K has a whopping sixteen total cores, eight physical and eight virtual. We'll soon see if the extra virtual cores of the Core i7 line make a difference for modern gaming. We've found in past benchmarking articles that Hyperthreading doesn't always provide a boost in gaming.
For our testing, we're using one benchmark test (3DMark Time Spy) and eight games: Crysis 3, Battlefield 4, Grid AutoSport, Far Cry 4, The Witcher 3, Fallout 4, Rise of the Tomb Raider, and DOOM. All benchmarks were run at a 2560x1440 resolution, which is becoming the new norm for high-performance gaming, and is generally quite easy for our GTX 1080 video card to handle. You might see CPU benchmarks run at 1920x1080 or lower resolutions (like the absurd 800x600), but our feeling is that whether or not these draw out more distinctions between CPUs because they present so little burden to GPUs is irrelevant when it comes to making decisions about products you are actually going to buy. If you're spending lots of money on CPUs and GPUs to run at 1080p, you're doing it the wrong way! See our Monitor Buyer's Guide for more advice on the monitors you should be gaming on today.
OK, time to get into some testing. To give us a bit of a baseline, we're going to give you the numbers generated by 3DMark Time Spy, the newest in a long line of easily-comparable benchmarks from FutureMark. It's now owned by UL, the respected testing company previously known as Underwriters Laboratories.
3DMark Time Spy
Time Spy is the latest in a long line of system benchmarks in the 3DMark family, and the first ot harness the power of Microsoft's DirectX 12. DX12 is a lower-level graphics API than its predecessor DX11, which means it's harder to code, but also allows developers to get "closer to the metal", i.e., the CPU. It should in theory take better advantage of all of a CPU's cores, as well as Hyperthreading.
To interpret the results, we suggest you focus on the grey bars (the CPU Score) , as the orange bars (the Graphics Score) are all within the margin of error, as they should be given no change in the video card. In the past we've found that Hyperthreading provides about a 50% boost in 3DMark benchmarks, and yet when we look at the 6600K and 6700K at 4.4GHz, the latter is only around 30% ahead. It seems Time Spy isn't making as much use of Hyperthreading as we would have guessed. Also take a look at the Core i7-6900K@4.4GHz. It's an impressive 93% faster than the Core i7-6700K, harnessing the power of its eight cores. If it were a Skylake-based chip rather than a Broadwell-based chip, it likely would have been 100% faster. Also note that it picks up 20% from overclocking, while the 6600K picks up 19% and the 6700K picks up just 7%, as the latter was already running at 4GHz to start with. Remember what we said, though: we had to draw the line somewhere, and we drew it at 4.4GHz.
OK, now it's time to get our game(s) on!