Intel Core i7-8700K and Core i5-8400 Processor Review – Coffee Lake

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Core i7-8700K Coffee Lake Overclocking

Overclocking the Intel Core i7-8700K Coffee Lake processor on the Gigabyte Z370 AORUS Gaming 7 motherboard ($249.99) with BIOS Version F4a is super simple and the Graphical User Interface (GUI) was easy to navigate and find what you needed to get to. There were a few minor issues we found on this early pre-public UEFI build and hopefully they’ll get them patched up on the next release version.

5100MHz Cinebench

We overclocked our Intel Core i7-8700K Processor up to 5.1 GHz by just raising the multiplier in the UEFI and changing no other settings. In just seconds we were running on the desktop and able to benchmark at 5.1 GHz with full stability.

5200MHz Cinebench

We pushed on and was able to hit 5.2 GHz by increased the multiplier up to 52x and changing nothing else in the UEFI. We could still run some benchmarks, but we wouldn’t call the system fully stable.

8700k 5300mhz

Just for fun we wanted to see if we could get into Windows and run any benchmarks at 5300MHz and we were amazed that we could get 5.3 GHz to boot and we were on the desktop at those clock speeds. It wasn’t stable enough to run Cinebench, but it was running!

After hitting 5.3 GHz and having some fun we got serious and started to monitor the temperatures closely to see if we were thermally throttling. The Corsair Hydro Series H105 water cooler ($114.99) is a pretty decent with its extra-thick 240mm radiator and dual SP120L fans, but we noticed that we were getting up over 95C on the individual cores. The Intel Core i7-8700K idles at a super cool 23-26C per core and then when the cores start running at 5,100 MHz they instantly jump up to around 90C, so good cooling is going to be needed for overclocking.

When we were running the AIDA64 stress test we noticed that the Package TDP hit 133 Watts (stock we only hit 75 Watts) and we did see on the Intel Extreme Tuning Utility (XTU) that the 8700K was thermal throttling. The good news is that despite XTU flickering the Thermal Throttling notice the clock speed and core voltage didn’t show that they were dropping. Due to temperature concerns we were more than happy with our 5.1 GHz overclock on the Core i7-8700K and it was solid enough to run every benchmark in our test suite at those speeds. That means we’ll be including benchmark results on the 8700K at stock speeds and all cores at 5.1GHz for this review!

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  • Jake40563

    I really hope that reviews are unbiased, however I noticed that power consumption of 8700k in overclocked mode was completely ignored or I may say omitted, why????

  • goldstone77

    It takes ~1 hour for liquid in a 240mm liquid cooler to absorb heat and become saturated. How does 5 min. AIDA64 show real world temperatures that the average user would find if he would run blender or handbrake for 1+ hours? How do you factor in the all core turbo boost of 4.7GHz and 145W into this equation for helping people come up with a proper cooling solution? 95W TDP hahaha

    • Nathan Kirsch

      So, the liquid in the cooler warms up a bit more than this. It’s not worth the time doing it when there are thousands of case and cooler options out there. We test on an open test bench anyway, so all of our temperature results are going to be different than most of what the readers will see at home. We quickly look at temps and move on. This is a CPU review and not a CPU cooler review!

      • goldstone77

        I agree that a CPU review should be about the CPU. But the cooling solutions and motherboard settings involved do change the results of tests, and I believe this should be noted in the review for clarity and transparency. So, in respect to your viewers do you feel it important to convey to them that your tests will vary from real world situations that the average user would encounter at home? As a viewer I would like to see statements like this incorporated in future reviews. Also, I wouldn’t mind seeing some real world scenarios with testing in a case with typical fans and using an air cooler with the processors TDP rating, and with the full array of motherboard settings. Just my 2 cents.

  • goldstone77

    Why did you disable turbo boost for your temp test, and enable it for your performance tests? You do realize that you are getting an all core turbo or 4.7GHz consuming 145W, and saying that the 8700K falls in line with your expectations of a 95W TDP. Gamers Nexus “Multi-core “enhancement” options are either enabled, disabled, or “auto” in motherboard BIOS, where “auto” has somewhat nebulous behavior, depending on board maker. Enabling multi-core enhancement means that the CPU ignores the Intel spec, instead locking all-core Turbo to the single-core Turbo speeds, which means a few things: (1) Higher voltage is now necessary, and therefore higher power draw and heat; (2) instability can be introduced to the system, as we observed in Blender on the ASUS Maximus X Hero with multi-core enhancement on the 8700K; (3) performance is bolstered in-step with higher all-core Turbo.”

    • Nathan Kirsch

      Testing was done on the Gigabyte Z370 Gaming 7 motherboard and we left multi-core enhancement to the default setting of ‘auto’ and that is off. This is not a CPU feature and is an overclocking feature done by the board makers. We did try multi-core enhancement with the 8400 on the Gaming 7 and found that it flat out didn’t work. Gigabyte Taiwan confirmed this and is fixing it for the next UEFI release. Since multi-core enhancement is not an Intel feature and varies between board manufactures the decision was made not to cover it. Multi-core enhancement in our opinion should be put in motherboard reviews when dealing with overclocking.

      • goldstone77

        Thanks for sharing that information. Jayz2cents ended up making another review after finding out his motherboard has “Multi-core enhancements” enable on the auto setting. And was told by the manufacturer it was turned off on auto setting. He confirmed to them it was in fact turn “on”. They said they will be putting out a bios change to disable it on auto.

  • IntelAMDNvidia
  • Dorian Kunch

    Really want to thank you Nate for including the old i7-2700 in the review. I have been holding out for that magical 2x the speed thing to manifest, probably there are others too. And it’s all gotta work; games and video processing.

  • Six_Tymes

    waiting for an 8350K