As I've written in the other thread, this is under a
stress test, an unrealistic scenario that is designed to test the limits of the cooling and power system. The MBP is a thin and light laptop and is not designed to be operated under such circumstances. And in fact, this is a good result, since it throttles less than some other laptops in the same category (for example, Dell XPS throttles down to 1.5Ghz, Razer Blade to 1.7Ghz and Asus Zenbook Pro to a whopping 1.3Ghz).
Most importantly, you will probably never experience this kind of throttling in a practical situation, unless you try playing games while transcoding a bunch of 4K videos or do something similarly silly. This is a stress test, designed to push the machine to an unreasonable limit. Its like testing a car by loading it up to the safely limit, chaining it to a tree and then pushing the throttle as hard as you can trying to get it up a gravel road up a hill.
The only purpose of this test is testing the limits, and its doing exactly what its supposed to do — clocking down to prevent damage. If you want a machine that can do better — start looking at large and heavy gaming and workstation laptops.
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My experience says that the i7 should win out in max performance...
Because Coffee Lake is clocked so weirdly compared to previous generations and it seems that it lacks a frequency limited for multicore operation, all of these CPUs should reach similar clocks in multi-core sustained operation. This was not the case with previous CPUs simply because Intel has placed a clock limit that stopped the CPU from getting higher. So yes, if what you do for living is encode videos or do raytracing on the CPU, the i9 is not worth it.
Where i9 is better though is burst performance, since its max turbo is higher.
Another thing brought up: both the CPU & GPU will thermal limit. That's actually not the case. Thermal control is something CPU controlled.
Thermal control on CPU and GPU works very similarly. Macs are a bit special in this regard anyway, since they have dedicated hardware that monitors all this stuff and controls power levels. Its simply that the management system priorities the GPU before the CPU. The assumption is as follows: if you are actively using the GPU, than that is probably the more critical component for the user experience. In most games for example, you won't notice if the CPU frequency goes down a bit, but throttling the GPU will have a clear noticeable effect.
1.8 on the frequency across multiple cores isn't bad. Single core performance will suffer, though...& that shouldn't matter for the most part as we will likely be single tasking high performance, unlike what this test demands.
Single core performance won't suffer much, simply because less cores are active. In the above video, the stress test sees CPU maintaining 28 Watts while running on 1.7-1.8Ghz all 6 cores. In another words, the combined sustained TDP for CPU and GPU is around 65 watts, which makes perfect sense for the 85 watt power adapter. These 28 watts though are more then sufficient to keep two CPU cores at above 4Ghz. I can't give you exact figures, since I've sold my i9 and currently waiting for the new model with Vega