Overclocking Intel Core i5 6600K to 4.2 GHz

The Skylake i5 is the 6th generation Core micro-architecture that has a lot of gaming power by default, especially the K series of CPUs. But, with only 4 cores and no hyper-threading, they are just not the right fit for some scenarios, especially video encoding. So, other than buying a new CPU (and board and maybe even RAM – as intriguing as it sounds), what can you do to get more performance? Overclock it! That’s what the K stands for, right? OverKlocK.

The stock clock is 3.5 GHz and a 3.6 GHz default OC when there’s load on all cores (why call it a 3.5 GHz CPU then?). The RAM is clocked at 2133 MHz, the max speed the Skylake memory controller supports. The few games I used for testing were run at 1080p and 1440p, the latter being my gaming resolution. Since my graphics card is an aging GTX 970, I’m pretty sure I won’t see much gain at 1440p. I also test video encoding and that’s where we’ll see the most improvements.

The graphics are set to a custom level where I can play comfortably, so they are not comparable to tests from other sites. The same settings are used for both resolutions.

Games 1080p

CPU 3.5 – RAM 2133
CPU 4.2 – RAM 2133
CPU 4.2 – RAM 2666
Rise of the Tomb Raider
86.46
86,07
86,90
RotTR: Mountain
101.20 (61.13)
100.53 (63.21)
101.56 (61.43)
RotTR: Syria
81.34 (43.78)
80.14 (43.98)
81.22 (49.89)
RotTR: Valley
76.04 (35.09)
76.56 (43.50)
76.79 ( 47.22)
Witcher 3
73.2 (65)
73.5 (65)
73.3 (67)
Dragon Age: Inquisition
54.6 (47.5)
55 (47.6)
54.2 (47.7)

It’s obvious that not much happened in the average FPS department. However, Rise of the Tomb Raider and Witcher 3 see a rise in the minimum FPS which is always nice, especially at a lower framerate.

Games 1440p

CPU 3.5 – RAM 2133
CPU 4.2 – RAM 2133
CPU 4.2 – RAM 2666
Rise of the Tomb Raider
56.49
56.25
56.42
RotTR: Mountain
66.05 (41.60)
65.71 (37.06)
65.87 (38.37)
RotTR: Syria
51.25 (38.05)
50.97 (36.45)
51.20 (39.28)
RotTR: Valley
51.30 (34.19)
51.17 (34.53)
51.33 (36.14)
Witcher 3
47.1 (42)
46.9 (41)
47.8 (42)
Dragon Age: Inquisition
37.2 (34.6)
37.5 (34.6)
37.4 (34.8)

At this resolution there’s no gain whatsoever, not that I expected any. Minimum framerates are a bit wonky and all over the place. Even though they are lower on the higher clocked CPU I attribute that to inaccuracies of measurement.

Encoding

The x264 Benchmark performs 4 encoding runs with two passes each. The first number is pass 1 and the second pass 2. Then I also encoded a 15-minute 1440p @ 30fps gameplay video of Rise of the Tomb Raider with TMPGEnc (x264 under the hood). This is how I encode my Youtube videos and here’s how I expect to see improvements from the additional 600 MHz.

 

CPU 3.5 – RAM 2133
CPU 4.2 – RAM 2133
CPU 4.2 – RAM 2666
x264 Run 1
48.04 / 13.81
55.59 / 16.16
56.49 / 16.15
x264 Run 2
47.90 / 13.83
55.05 / 16.15
56.12 / 16.16
x264 Run 3
48.15 / 13.83
55.11 / 16.16
56.15 / 16.14
x264 Run 4
48.06 / 13.82
55.12 / 16.17
56.02 / 16.13
15 Minute Video
41:58
36:43
36:01

More speed across the board. In this case it is also worth noting that the additional RAM MHz do provide another speed increase. Doing some math, one minute of 1440p gameplay took 2 minutes and 48 seconds on the stock configuration and 2 minutes and 24 seconds in the overclocked config. That doesn’t sound like much, 24 seconds win for one minute of video, but in total, as you can see, it sums up to 6 minutes for a 15-minute video clip. Going a step further, my Tomb Raider videos are about 40 minutes long and that amounts in roughly 15 minutes of saving.

Summary

In total, no real win in games but a lot in video encoding. So, in order to also benefit in games a bit more I will have to kick my GPU in the butt a bit, so stay tuned for that. Some technical notes on the overclocking settings.
  • BCLK: 100
  • Multi: 42
  • CPU Core Voltage: +0.050 V offset
  • SA Voltage: 1.110 V
  • IO Voltage: 1.130 V
  • RAM Voltage: 1.2V
  • RAM Ratio: 133×20

The CPU did 4.1 GHz on stock voltage and then required more juice for the next 100 MHz. Since I was happy enough with 600 MHz more on top of the default 3.6 GHz I stopped there. More voltage also means more heat and higher power consumption. At some point, the gain in speed outlives the amount of energy saved by the whole system from the shorter encoding duration.

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