Intel Skylake Core i7-6700K IPC & Overclocking Review

Today we finally get to share with you our Intel Skylake experiences. As we like to, we are going to focus on Instructions Per Clock / IPC and overclocking this new CPU architecture. We hope to give our readers a definitive answer to whether or not it is time to make the jump to a new desktop PC platform.


Overclocking Skylake

We have spent the better part of a week overclocking our Intel Core i7-6700K Skylake processor, and have learned a few things. First and foremost is that it does not look like a "5GHz" chip that we were promised back with Devil's Canyon. Of course, Intel has not in any way made that an expectation, at least not verbally this time. I do however think that a lot of enthusiasts are expecting this however. 5GHz is not happening for a long time stable overclock unless there are some very special "golden" processors out there.

Our Skylake processor seems to hit a stability wall very quickly. If you will notice that our benchmarks reflect a 4.8GHz/3600MHz overclock at a 1.42v Core Voltage. Before testing with those clocks I used our usual Prime95 stress testing to find our stable clocks. I ran Prime95 for about 3 hours and called it good to move forward for benchmark testing, to return to stability testing later on. When I got to running our Handbrake tests, the processor failed almost immediately. The Handbrake program would crash rather than the system BSODing however. I had to increase voltage to 1.45v to get it to complete those short Handbrake tests. Moving on with collecting data I finished up and went back to finding out more about long term overclocked stability.

At 4.8GHz/3600MHz at 1.45v we were seeing per core temperatures bump into the upper 90C range. I fought with it at 4.8GHz for a day but could not find anything to make it stable to our standards. Handbrake is this CPU's nemesis. And considering that it is a widely used program, and we actually use it for a "backup" stability test, I think that it must be program that can be run on an overclocked CPU with success. Handbrake stability just was not happening at 4.8GHz, even taking the RAM down to 2133MHz did not help. I tapped out and started seeing if I could get 4.7GHz/3600Mhz stable.

Starting with a 1.42v Core Voltage and a 4.7/3600 overclock, everything was smooth as butter, but I was still seeing high Skylake CPU core temperatures. So, I backed the Core Voltage down to 1.30v and started working my way up from there. I found that my Skylake processor, on this ASUS Z170-Deluxe motherboard, is rock solid at 1.344 actual vCore. (Setting was 1.32v in the BIOS.)

So after toying with it for a while, I set the system up to do a stability run at 4.7GHz/3600MHz at 1.32v vCore, and 1.35v (spec) memory voltage. The screen shot below shows you a 23 hour run of Prime95. (But Kyle said Prime95 was not the problem! You would be correct.) With Prime95 running I then ran multiple Blu-ray encodes as well. Handbrake is utilizing areas of the logic that Prime95 is not, and vice versa, so I figure running those simultaneously would be fun for the whole family. I also ran multiple full length Bluray encodes as well with no other programs running. (Do note that the CPU-Z core voltage data is incorrect, so just ignore that. Hopefully we will see that corrected in a future version if it has not already been updated by the time you read this.)

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Consider for a moment that I was seeing 95C core temperatures trying my best to fight for a 4.8GHz overclock. While my pride was a bit hurt at having to move back to a 4.7GHz, the loss of that 100MHz paid off in spades when it comes to core voltage and per core temperatures. The max temperature values of 76/74/79/82C are something get excited about. Turning off HyperThreading and I saw per core temps drop by another 8 to 10C. I was hoping that turning off HyperThreading would get me to the elusive 4.8GHz, but that did not happen though. The Skylake processor acted very much the same whether HT was on or off aside from the lower temperatures.

With this Corsair Dominator Platinum RAM, I never had an issue either, although this memory is not exactly for a budget build. In fact, RAM speed seemed to have little or no impact on the CPU core overclocking abilities. (And there are some reasons for that, but we will save those for the motherboard reviews.)

Getting this Skylake CPU to 4.7/3600 on air should be possible if you have air conditioning.

One thing we did not use at all on this Skylake CPU was the integrated video. I was told specifically to not expect to overclock this CPU for much anything if I was using the integrated video. It is HOT and will kill your chances of getting some decent overclocks.

There was also not a lot of tweaking to be done on this ASUS Z170-Deluxe motherboard either. Basically just toggle your CPU multiplier, set your CPU voltage, set your RAM clock, set your RAM voltage, and you are done. Asking ASUS if they thought I was getting everything out of the motherboard and going back and explaining a few days of processes I had gone through, this was their reply:

No special tricks really for this platform on air/water cooling, it really comes down to the main three rails (Vcore and then SA and IO for memory side). I think you’ve worked it all out. Only thing I did not write much about is cache clocking آ– which one can add in after everything else is stable. Maybe a non-worthwhile trade-off with core/memory when approaching max clocks on those domains however, so I did not give it priority. I have heard some CPUs can get cache freq a couple of ratios below core.

ASUS did tell me that my Skylake processor was running stable at one of the lowest core voltages that it had seen, so keep that in mind when you go to tune yours.

It is worth noting here that I never had to touch my Input Voltage like we have seen on our recent Haswell processors. This may or may not be the case with your CPU or the DIMMs you are using. But the integrated memory controller looks to be rock solid on the Skylake processors.