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I'm going to say this straight away – overclocking with Skylake is fun! Intel's decisions to remove the voltage regulator from the CPU and also completely open up the BCLK make for plenty of overclocking and tweaking possibilities with a variety of approaches.
The constricted time scale that we had to work with our Skylake samples forced us to gravitate our overclocking testing around the core ratio route with a static 100MHz BCLK. This is the most straightforward way of overclocking and is likely to be used by those who want quick, simple gains with very little effort expenditure.
Overclocking enthusiasts will mix their efforts between adjusting the BCLK and CPU core ratios in order to squeeze as much performance as possible from a chip. That is something that we will look at in future articles.
Intel Core i7-6700K Overclocking
We tested a variety overclocking configurations to find the best settings for our chip. In order to keep temperatures in check and maintain voltages at what we are told are safe levels for 24/7 usage, the maximum CPU Core voltage was set at 1.40V. Empirical testing showed that Asus' level 5 LLC profile resulted in a load core voltage closest to our selected 1.40V level – the 6700K chip was delivered 1.392V under full load with a 1.40V Core voltage and level 5 LLC settings.
Gains can be had from running the PCH voltage at 1.1V, and increasing the CPU standby and PLL voltages to around 1.20V and 1.45V, respectively. With that said, we found that simply applying a manual VCore level, adjusting the LLC settings, and removing power delivery thresholds resulted in equally-good overclocking gains.
It is also worth noting that the CPU cache is now driven by the single core voltage level, so finding a voltage sweet-spot for that setting is not required. Overclocking headroom allows the cache frequency to be run very closely to the increased CPU frequency.
We managed a comfortable 4.8GHz from our retail 6700K chip while using a 1.4V core voltage (which translated into 1.392V under load with our LLC settings). This frequency was perfectly stable for extended periods of stress testing and temperature levels were well below the worrying 90°C mark.
Speaking to other system integrators with Skylake overclocking experience, around 4.7-4.8GHz with a 1.4V core voltage seems to be a comfortable level for many Core i7-6700K chips. Knocking the voltage down towards the 1.35V level should deliver 4.5GHz comfortably. The i7 overclocking gains seem consistent, controllable from a temperature perspective, and fairly straightforward to manage.
It's worth pointing out that both of the CPUs we tested are retail version, not engineering samples that have shown differing overclocking gains with past processor generations (Haswell).
In order to make a direct comparison with our 4.7GHz Devil's Canyon chip, we decided to run our Core i7-6700K testing at 4.7GHz. This used the same settings as the 4.8GHz profile mentioned about – 1.40V Core voltage, level 5 LLC, and removed power thresholds.
We set the CPU cache frequency at 4.5GHz in order to open performance gains but not push it to a point where stability is compromised.
Note: CPU-Z does not identify the correct CPU core voltage 100% of the time. We recommend using the motherboard vendor's software utility to record system voltages until a new release of CPU-Z launches.
Intel Core i5-6600K Overclocking
Overclocking our Core i5-6600K CPU was less effective than the i7-6700K. Despite being fed with 1.4V initially, the chip would not hold stability on all cores at a frequency of 4.6GHz via the 46x100MHz route. There was an occasional drop in load from one of the four cores, indicating that the overclock was not fully stable.
We accepted the frequency limit of 4.5GHz and were able to dial down CPU core voltage to 1.35V. CPU cache frequency was set at 4.5GHz.
