The Intel Kaby Lake-X i7 7740X and i5 7640X Review: The New Single-Threaded Champion, OC to 5GHz
by Ian Cutress on July 24, 2017 8:30 AM EST- Posted in
- CPUs
- Intel
- Kaby Lake
- X299
- Basin Falls
- Kaby Lake-X
- i7-7740X
- i5-7640X
Power Consumption
With the two Kaby Lake-X processors, the main comparison for power consumption is going to be against their Kaby Lake-S counterparts on the mainstream platform. For an extra 100 MHz, Intel is moving from a 95W TDP to a 112W TDP, indicating that these processors will need better cooling – but when we tested KBL-S we were rather surprised by the power, especially on the Core i5.
The Core i5-7640X almost perfectly matches up with its Core i5 counterparts, even beating the Core i5-7600K in every situation but especially at load. For users who want to overclock near to the official TDP, it looks like there’s some headroom (other circumstances permitting). The Core i7-7740X is noticeably more power hungry at full load, hitting 79W, but lower than the Core i7-7700K at 87W.
Overclocking to 5.0 GHz
One of the elements promoted at the launch of Basin Falls was overclockability: Intel ran a private invite-only extreme overclocking workshop with sub-zero coolants that week, which was then followed by ASUS and GIGABYTE both stepping it up another gear by using liquid helium rather than liquid nitrogen. For some of these chips, the colder the better, and liquid helium is going to be limit for cooling (and cost) as there is inherent difficulty in using sub-zero coolants for records.
Those sub-zero events for records are just on single benchmarks, or single frequency records, and are not meant to be run at those speeds all day every day. This makes the air and water overclocking potential of the CPUs more important for regular users and enthusiasts.
When Kaby Lake-S was launched, we saw good overclocking performance on the Core i7-7700K: our set of 4.2 GHz base processors reached a range between 4.6 to 4.8 GHz, arguably giving a 8-15% overclock and given some of the numbers we had seen in the wild, the consistency between the processors meant that most of the 7700K CPUs could reach that amount. One of the reasons for such good performance on these CPUs was that Intel had incorporated a new feature for overclocking, the AVX offset. This allows overclockers to reduce the frequency that AVX code runs at, as this can be a limiting factor when it comes to a stable overclock. This feature is in Kaby Lake-X as well.
The end result is that the Core i7-7740X went one further in our testing, and hit 5.0 GHz all-cores at 1.25V, and completed our CPU testing suite with a -10 AVX offset. We went for 5.1 GHz all-core, up to 1.35 volts, but the temperatures were getting high and the system was still not stable. 5.0 GHz is a very respectable result, even if we only have a sample of one.
The results at 5.0 GHz are as follows. Gain is absolute for the benchmark for the 5.0 GHz value, with anything within 2.0% listed in orange. Green indicates a win for the faster chip.
Comparison: Intel Core i7-7740X at Stock vs 5 GHz | |||
4.3 GHz Base 4.5 GHz Turbo Auto AVX |
5.0 GHz Base 5.0 GHz Turbo 4.0 GHz AVX |
||
Score / Time | Web Benchmarks | Score / Time | Gain |
135 ms | Sunspider | 133 ms | +1.6% |
622 ms | Kraken | 642 ms | -3.1% |
45485 | Octane | 45279 | -0.5% |
561 | WebXPRT15 | 570 | +1.5% |
System Tests | |||
2229 ms | PDF Opening | 2055 ms | +8.5% |
46.172 s | FCAT | 45.656 s | +1.1% |
1287 | 3DPM 2.1 | 1429 | +11.0% |
282 s | Dolphin v5 | 280 s | +0.7% |
891.56 s | Agisoft Total | 830.06 s | +7.4% |
Rendering | |||
2474593 | Corona | 2660002 | +7.5% |
436 s | Blender | 485 s | -10.1% |
195 | Cinebench 15 ST | 215 | +10.6% |
986 | Cinebench 15 MT | 1084 | +10.0% |
Encoding | |||
27433 | 7-zip | 29433 | +8.9% |
48.698 s | WinRAR | 46.633 s | +4.4% |
5.5 GB/s | AES | 6.2 GB/s | +12.7% |
25.2 FPS | Handbrake HEVC | 22.6 FPS | -10.2% |
Office Tests | |||
4878 | PCMark8 Creative | 5084 | +4.2% |
4844 | PCMark8 Home | 5071 | +4.7% |
4110 | PCMark8 Work | 3984 | +3.2% |
19.45 per day | Chrome Compile | 17.70 per day | -9.0% |
GTX 1080 | |||
72.56 FPS | 1080p Ashes Av | 76.19 FPS | +4.8% |
53.95 FPS | 1080p Ashes 99% | 55.45 FPS | +2.7% |
62.30 FPS | 4K Ashes Av | 63.46 FPS | +1.8% |
41.24 FPS | 4K Ashes 99% | 40.79 FPS | -1.1% |
103.66 FPS | 1080p RoTR-1 Av | 106.9 FPS | +3.0% |
85.14 FPS | 1080p RoTR-1 99% | 85.88 FPS | +0.9% |
61.60 FPS | 4K RoTR-1 Av | 61.33 FPS | -0.4% |
50.25 FPS | 4K RoTR-1 99% | 50.43 FPS | +0.3% |
There are a few obvious trends, and a couple of red flags. Most benchmarks split themselves into two groups: benchmarks with a heavy CPU component tend to get a 4-12% gain when overclocked, and those that require a lot of DRAM involvement or AVX tend to be in the 2% region. The red flags are the three big 9-10% loss values for CPU heavy benchmarks, Blender, Handbrake HEVC and Chrome Compilation.
All three benchmarks are sizable workloads with sustained high frequencies throughout, and have heavy AVX components as well. The 4.0 GHz setting for AVX could account for most of that difference, however other AVX benchmarks in our testing (Corona, Cinebench, elements of PCMark, Agisoft) do not have the same effect. The only real difference here is time: the amount of time each benchmark stays at a sustained load.
The three that had the biggest dips are our longest benchmarks: Blender at 8 minutes, Handbrake HEVC at 25 minutes, and the Chrome Compile at over an hour. In this case it seems we are hitting thermal limits for the power delivery, as explained by Igor Wallossek over at Tom's Hardware. He tested an upcoming theory that the early X299 boards are not up to the task for cooling VRMs at heavy load, and through analysis he determined that this was likely to occur in heavily overclocked scenarios. His data showed that the Skylake systems he tested, when overclocked, would hit thermal limits, come back down, and then ramp up again in a cyclical manner. He tested Skylake-X, which draws a lot more power overclocked than our KBL-X setup here, so it likely isn't affecting our setup as much, but still enough for certain benchmarks. I fully suspect we will see second-wave X299 motherboards with substantial heatsinks on the power delivery to overcome this.
More testing is needed, especially in upcoming X299 motherboard reviews. We used an early X299 prototype for our CPU testing here, and a Gaming 9 motherboard on the GPU tests (which showed little variation and no problems). We did take power numbers for this setup but when looking back on the results, they seemed off so we need to go back and re-test those.
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mapesdhs - Monday, July 24, 2017 - link
Let the memes collide, focus the memetic radiation, aim it at IBM and get them to jump into the x86 battle. :Ddgz - Monday, July 24, 2017 - link
Man, I could really use an edit button. my brain has shit itselfmapesdhs - Monday, July 24, 2017 - link
Have you ever posted a correction because of a typo, then realised there was a typo in the correction? At that point my head explodes. :DGlock24 - Monday, July 24, 2017 - link
"The second is for professionals that know that their code cannot take advantage of hyperthreading and are happy with the performance. Perhaps in light of a hyperthreading bug (which is severely limited to minor niche edge cases), Intel felt a non-HT version was required."This does not make any sense. All motherboards I've used since Hyper Threading exists (yes, all the way back to the P4) lets you disable HT. There is really no reason for the X299 i5 to exist.
Ian Cutress - Monday, July 24, 2017 - link
Even if the i5 was $90-$100 cheaper? Why offer i5s at all?yeeeeman - Monday, July 24, 2017 - link
First interesting point to extract from this review is that i7 2600K is still good enough for most gaming tasks. Another point that we can extract is that games are not optimized for more than 4 core so all AMD offerings are yet to show what they are capable of, since all of them have more than 4 cores / 8 threads.I think single threading argument absolute performance argument is plain air, because the differences in single thread performance between all top CPUs that you can currently buy is slim, very slim. Kaby Lake CPUs are best in this just because they are sold with high clocks out of the box, but this doesn't mean that if AMD tweaks its CPUs and pushes them to 5Ghz it won't get back the crown. Also, in a very short time there will be another uArch and another CPU that will have again better single threaded performance so it is a race without end and without reason.
What is more relevant is the multi-core race, which sooner or later will end up being used more and more by games and software in general. And when games will move to over 4 core usage then all these 4 cores / 8 threads overpriced "monsters" will become useless. That is why I am saying that AMD has some real gems on their hands with the Ryzen family. I bet you that the R7 1700 will be a much better/competent CPU in 3 years time compared to 7700K or whatever you are reviewing here. Dirt cheap, push it to 4Ghz and forget about it.
Icehawk - Monday, July 24, 2017 - link
They have been saying for years that we will use more cores. Here we are almost 20 years down the road and there are few non professional apps and almost no games that use more than 4 cores and the vast majority use just two. Yes, more cores help with running multiple apps & instances but if we are just looking at the performance of the focused app less cores and more MHz is still the winner. From all I have read the two issues are that not everything is parallelizable and that coding for more cores/threads is more difficult and neither of those are going away.mapesdhs - Monday, July 24, 2017 - link
Thing is, until now there hasn't been a mainstream-affordable solution. It's true that parallel coding requires greater skill, but that being the case then the edu system should be teaching those skills. Instead the time is wasted on gender studies nonsense. Intel could have kick started this whole thing years ago by releasing the 3930K for what it actually was, an 8-core CPU (it has 2 cores disabled), but they didn't have to because back then AMD couldn't even compete with mid-range SB 2500K (hence why they never bothered with a 6-core for mainstream chipsets). One could argue the lack of market sw evolvement to exploit more cores is Intel's fault, they could have helped promote it a long time ago.cocochanel - Tuesday, July 25, 2017 - link
+1!!!twtech - Monday, July 24, 2017 - link
What can these chips do with a nice watercooling setup, and a goal of 24x7 stability? Maybe 4.7? 4.8?These seem like pretty moderate OCs overall, but I guess we were a bit spoiled by Sandy Bridge, etc., where a 1GHz overclock wasn't out of the question.