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Overclocking
One of the main attractions of Intel's Z-series chipsets is the ability to turn up the clocks with its unlocked CPUs, so we put the Z270X-Gaming 5's various paths to higher clocks to the test.

During our initial testing of the Gaming 5, we discovered that the board wants to feed the Core i7-7700K with 1.38V of juice to hit 4.5 GHz under our Prime95 Small FFTs load. At those clock and voltage settings, our chip throttled under our Corsair 280-mm liquid cooler—not an encouraging experience. It seems this may be a consequence of Intel's conservatism with the stock VID it bakes into K-series chips to account for production variances, however, not a fault of Gigabyte's firmware.

Just for kicks, we dove into the firmware at this point and set a 1.2V fixed Vcore with stock multipliers left intact. Even though the chip wasn't stable at those settings, it didn't put nearly as much of a strain on our CLC, reaching about 70° C. We then set load-line calibration to High and re-ran our 1.2V test, at which point the chip was stable. As a baseline, the stock VID Intel baked into our chip wasn't especially useful.

Given our manual overclocking results in our Core i7-7700K review, it only made sense to start out with the board's "i7-7700K 4.8 GHz" CPU Upgrade profile. However, our board wouldn't even successfully boot to Windows with that pre-baked profile enabled. We reset the firmware to its optimized defaults and decided to move onto the company's Easy Tune Windows software.

We kicked off Easy Tune's iterative overclocking feature from within Windows. After a reboot, Easy Tune set a 47x all-core Turbo multiplier and successfully completed its built-in stress test. The utility didn't tell us the voltage it chose to get there, however, so we dug into Easy Tune and found that the auto-OC tool chose an eyebrow-raising 1.4V Vcore for the Core i7-7700K.

Though we'd generally be making a run for the "default settings" button with anything above a 1.35V Vcore on a 14-nm Intel chip, we decided to trust the board's instincts and fired up our Prime95 Small FFTs torture test. Strangely, the Vcore value dropped way beneath Gigabyte's 1.4V choice during that test, hovering more in the 1.28V-1.3V range. At those (possibly Vdroop-induced) values, our chip had no trouble staying cool or stable. Removing the Prime95 load took the Vcore back up to that concerning 1.4V value, though, so we returned the Easy Tune software to its defaults.

With all of Gigabyte's automatic overclocking profiles exhausted, we returned all of the board's software and firmware settings to their defaults (save the XMP profile for our DDR4-3866 memory) and started tweaking manually. After some trial and error, we arrived at a 4.8 GHz overclock with a fixed 1.32V Vcore and a High load-line calibration setting. Higher clock speeds resulted in instability, and though our chip would certainly boot at 4.9 GHz, no amount of voltage made it stable under our Prime95 load before we ran into thermal throttling.  

Setting a fixed voltage isn't ideal for long-term use of a PC, though, since it increases power usage and heat production at idle. We much prefer adaptive voltage control during overclocking. In this mode, the motherboard can dial in more voltage as needed under an overclocked load with a user-configured offset value. At idle, it can still dial back voltage to save power. Gigabyte has at least clarified how to enable voltage offsets in the Gaming 5's firmware tooltips (set Normal in the CPU Vcore field), but it's still not clear to us what relationship the word "Normal" has with adaptive voltage control. For rank amateur overclockers, this obfuscation might prove confusing. We much prefer Asus' and MSI's standard lingo for these voltage modes: "manual," "offset," and "adaptive."

Still, once we had the CPU Vcore parameter set to "Normal," it was easy enough to dial in a -0.060V offset from the board's 1.38V stock value to hit our 1.32V stable Vcore. We didn't even need to dial in any load-line calibration at these settings.

We also should praise the Gaming 5's stability with the exotic DDR4-3866 memory that G.Skill sent us to pair with the Core i7-7700K in our review. We only had to flip on that kit's XMP profile to get blazing-fast memory speeds with perfect stability. That's impressive for such a high-speed DDR4 kit. As far as we could tell, the Gaming 5 didn't goose the Core i7-7700K's multipliers when we enabled our memory's XMP profile, as well—a welcome improvement.

Once we figured out how to control the Z270X-Gaming 5's core voltage in our preferred manner, overclocking proved easy and stable. Folks who'd rather let the motherboard do all the work, whether through an iterative overclocking process or through pre-baked profiles, may come away disappointed by this board. Amateurs may also have trouble deciphering Gigabyte's confusing names for common voltage-control modes, as well.