The Intel Core i7-4790K processor starts out life with a 4.0GHz base clock and can boost up to 4.4GHz. We heard that reaching 4.7GHz should be easy for most platforms with high-end air coolers or water cooling. For this review we wanted to see what we could hit with the Corsair H105 water cooler and we were hoping that the rumors of 5GHz Devil’s Canyon processors with water cooling would prove to be true.
We used the ASUS overclocking assistant on the Z97-A motherboard and was able to reach 4.59GHz in just a matter of seconds. The ASUS board automatically bumped up the multiplier from 44 to 45 and increased the Bus Speed from 100MHz to 102MHz as you can see in the screenshot above. It looks like we are off to a great start, but this is only 190MHz higher than the turbo clock speeds of the Core i7-4790K Devil’s Canyon processor.
We got into the ASUS Z97-A UEFI and manually did the overclock in AI Tweaker. We just cranked up the vCore and kept raising the multiplier until we got to 1.40V on the core and the system became unstable. By doing this we were able to enter Windows 8.1 and run a few benchmarks at 4.9GHz with 1.35V, but we just couldn’t get it fully stable and we didn’t want to go over 1.4V on the first few days that the 4790K was in our hands.
We ended up settling for 4.7GHz as that was the highest stable overclock that we could achieve on this processor. We were able to do this by leaving everything in the UEFI/BIOS untouched and just raising the multiplier up from auto to 47. It appears that the ASUS Z97-A automatically increases the voltage and in this situation we were running at 1.351V on the core. This was the easiest 4.7GHz overclock that we have had on any Haswell processor!
This just happens to be the top overclock for our Core i7-4770K processor as well, so when it comes to overclocking performance the Core i7-4770K and Core i7-4790K appear to be about the same. We don’t have any retail 4790K chips to play around with though, so our opinion is based on our experience with our engineering sample.
With the Intel Core i7-4970K Devil’s Canyon processor running 4.7GHz we were able to score 946 on the CPU test in Cinebench. We got a score of 900 stock, so this is a modest 5% performance gain as we are only overclocking 300MHz as the turbo clocks on this chip are at 4.4GHz. A 300MHz clock increase from 4400MHz is a 6.4% increase, so this is about what you’d expect to see.
At 4.7 GHz we saw the temperatures hit 76C, which isn’t bad considering Haswell and Devil’s Canyon don’t start throttling till 95C. It looks like the Next-Generation Polymer Thermal Interface Material (NGPTIM) that is being used on the Intel Core i7-4790K and Core i5-4690K processors really does help out.