Intel i5-8400 review – the best new gaming CPU in years

 In Technology

I’ve been hearing complaints about Core i5 ‘only’ having four CPU cores ever since Ryzen 5 came to market, and for good reason. If you’re just playing games, the chips are good and have arguably been the best value Intel processors, but do something more complex than gaming (like livestreaming or CPU-based video encoding) and a 4-core/4-thread (4C4T) chip can really start to bog down. With AMD offering 6C12T Ryzen 5 parts for around $200, Core i5 has become increasingly difficult to recommend. Intel’s solution to this problem is now here, thanks to its 8th Gen Core i5 processors (aka, Coffee Lake or CFL).

I covered more of the details of the Coffee Lake launch in the Core i7-8700K review, but this is the biggest generational improvement in Intel’s mainstream CPU line since the mainstream/enthusiast split that occurred with the 1st Gen Core i7 in 2010. Core i7 and Core i5 both get 50 percent more cores/threads, without a drop in clockspeeds, and Core i3 basically takes the previous generation Core i5’s place as a 4C4T part. If you’re still running a 2nd or 3rd—or even 4th—Gen Core processor, it’s finally time to upgrade. And just like AMD’s Ryzen 5, Intel has a compelling Core i5 model available for under $200, the i5-8400.

It’s telling that Intel didn’t even feel the need to send out the unlocked Core i5-8600K this round. That chip would require an aftermarket cooling solution, bringing the total price closer to $300. The i5-8400 meanwhile includes an Intel cooler and fan for $190. That’s a great start, but what about clockspeeds? If you look back at Kaby Lake’s i5-7400, the maximum turbo clock was a tame 3.5GHz, with $20 more getting the i5-7500 and a 3.8GHz turbo. The i5-8400 has an impressively high 4.0GHz turbo, but the base clock of 2.8GHz might scare some away. Rest easy, as the CPU will actually run at 4.0GHz on one core, 3.9GHz with 2-4 cores loaded, and 3.8GHz with all six cores loaded to capacity—and though it might exceed the nominal 65W TDP, it didn’t get overly hot. That means in addition to 50 percent more cores relative to Kaby Lake, you also get the same or higher clockspeeds.

There are a few things you’ll need to know before running out and buying a Core i5-8400. First, Intel is serious about locking down the clockspeed. I tried adjusting the BCLCK in the BIOS to see if I couldn’t squeeze a few more percent out of the chip. Nope—nada! Any setting other than ‘auto’ or 100MHz failed to POST. But you’re not completely blocked from improving performance, as you can raise the uncore clock from the default 2.8GHz to 4.0GHz and it did appear to improve performance a few percent. But if you want an unlocked Intel, the K-series (or X-series) parts are the only way to get that.

The other major issue a lot of people will have is that Coffee Lake processors require a new motherboard and a 300-series chipset. Right now, that means Z370, which , there is at least one fly in the ointment, and that’s the chipset/motherboard requirements. Coffee Lake uses the same LGA1151 socket as Kaby Lake and Skylake, but it requires a new 300-series chipset (currently only Z370). That Z270 motherboard you purchased earlier this year? Yeah, tough luck—despite earlier rumors that Coffee Lake would work in existing motherboards, that didn’t actually pan out. What’s more, you can’t bring your existing Skylake or Kaby Lake chip along and put it in a Z370 board.

This is due to modified power requirements on Coffee Lake—and let’s be clear, the pin-outs on the Coffee Lake and Kaby Lake processors are different, to the point that if you place a KBL chip in a Z370 board, or a CFL chip in a Z270 board, you could actually fry the chip. (I’m not planning on trying it, needless to say.) But the real question is whether Intel actually needed to modify the pinouts in the first place. I suspect not, and keeping the same socket while changing the pinouts seems like a very bad idea regardless.

The net result is that if you want a Coffee Lake processor, you’ll also need a new motherboard. As for the Z370 chipset, in terms of features and functionality it appears to be identical to Z270—just with some updated microcode that only recognizes Coffee Lake processors. There are no extra PCIe lanes, USB ports, or anything else that I could see.

It’s a bit sad to see Z270 and Kaby Lake come and go so quickly. Obviously, they’re not completely obsolete just because something new exists, but these were good CPUs and good motherboards. The Z170 launch back with Skylake in 2015 was a bit rocky, and by comparison Z270 was smooth sailing. Now, all of those designs need to be scuttled, to be replaced by Z370 chipsets probably sitting in otherwise nearly identical designs. RIP, Z270….

The full list of test platforms and hardware is up and to the right, but the only real change we’ve made for Coffee Lake is to swap our Z270 board out for a Z370 model. Gigabyte sent its Aorus Z370 Gaming 7 motherboard, an attractive high-end design with premium audio and three M.2 slots for NVMe storage. For testing, I used the F4a BIOS revision. All test systems also use fast DDR4-3200 memory to provide optimal performance, with M.2 NVMe SSD storage for the OS and applications, and games stored on a large 2TB SATA SSD as a secondary drive.

Nvidia’s GeForce GTX 1080 Ti Founders Edition graphics card was selected to help differentiate the CPUs in gaming benchmarks, with a chosen test resolution of 1920×1080 at ultra/maximum quality settings. The resolution allows for faster CPUs to make a difference, as higher resolutions will move the bottleneck to the graphics card, and even at 1080p ultra some games still end up GPU limited. If you think testing at 4K instead of 1080p would be better, just look at the performance charts for The Witcher 3 and try to decide which CPU is ‘best’ for gaming.

Finally, a quick word on the charts. You’ll notice a ‘i5-8400 OC’ entry in the graphs … but isn’t this chip multiplier locked? Yes it is, but you still have the option to tweak the uncore clockspeed a bit. By default it’s set to 2.8GHz, and I had no trouble running it at 4.0GHz. I also played around with CPU multipliers to see if I could force the CPU to always run at 4.0GHz, but at least on the Gigabyte board that didn’t appear to work. Still, bumping up the uncore clock does help a bit, and that’s what the ‘OC’ entries represent.

Core i5-8400 gaming performance

Take your existing Core i5 processors and add 50 percent more cores, and what does that give you? For games that already hit maximum performance on an i5-7600K (as an example), it won’t do much, but there are an increasing number of games that will show small to moderate gains with more cores and/or threads. Generally speaking, Hyper-Threading on an Intel CPU core gives you about a 20-30 percent boost in potential throughput, so having six full cores running six threads is actually going to be faster than four cores and eight threads—at least at the same clockspeed. Since the i5-8400 is clocked a bit lower than the i7-7700K, it’s not quite a direct replacement, but as you’ll see in the benchmarks, there are numerous games where the newcomer i5 beats the previous generation i7.

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In the overall average gaming performance metric, the ‘budget’ Coffee Lake i5-8400 ends up beating the former champion i7-7700K. Digging into the individual tests shows how this happens. There are only two games where the i5-8400 doesn’t deliver equal or better performance than a (stock) i7-7700K: Far Cry Primal (a four percent deficit) and Dawn of War 3 (a larger 13 percent deficit). Everything else is either tied or slightly favors the i5-8400. Dishonored 2 is the biggest win, with an 11 percent lead, followed by Battlefield 1 with an eight percent improvement. Civilization VI and Hitman show a small four percent lead, and that gives the overall one percent lead—effectively a tie, but at half the price (after you add a cooler) that’s still great news. Minimum framerates are a bit more erratic, though again the i5-8400 ekes out a one percent average lead.

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