Exterior GPU Testing: GTX 1080 in a Field + Core i7-8550U Ultraportable

Last year we looked briefly at external GPUs when we tested the Aorus GTX 1070 Gaming Box, which is attached to an ultraportable with Kaby Lake drive. Now that Intel's 8th generation CPUs are widespread in a number of ultrabooks with significant performance gains, it's the perfect time to revisit eGPUs and see if the hard CPU bottleneck still exists in most games.

As a brief summary, we last tested the GTX 1070 Gaming Box, which is connected to a Lenovo ThinkPad X1 Carbon via Thunderbolt 3. The gaming box contains a full desktop GTX 1070 GPU, but the weak Core i5-7200U with only two cores and four threads was a bottleneck in essentially all of the games we tested. The eGPU turned the ThinkPad from a slim ultra portable into a real one Slot machines with enough power, but the full performance of the GeForce GTX 1070 has by no means been unleashed.

In fact, the ultra-portable GTX 1070 eGPU + laptop combination was typically 30 to 50 percent slower than a conventional GTX 1070 gaming laptop and could be up to 65 percent slower for CPU-limited games. Stuttering was also a noticeable problem in some (but not all) of the games I tested with, which contributed to weak 1% low frame rates.

In most games, the GTX 1070 eGPU was slower than a GTX 1060 gaming laptop and often clear when comparing these crucial 1% low scores. Most of it was again due to the CPU bottleneck and bandwidth limitations of Thunderbolt 3. After all, Thunderbolt 3 only offers the GPU up to PCIe 3.0 x4 minus a certain amount of protocol.

In this eGPU revision, we continue the search for the ultimate portable gaming setup and increase the use in two ways:

First, Gigabyte kindly exchanged our GTX 1070 gaming box for its newer and faster Aorus GTX 1080 gaming box. These eGPUs come with an installed graphics card and are expected to be available in retail stores for around $ 700. However, given the current lack of GPU and price increases, these boxes are rare. Hopefully, when the graphics card market returns to normal, these boxes will become more available.

The GTX 1080 gaming box is pretty similar to its predecessor, so we won't be talking much about design and construction as it is basically the same as before. Important things to consider are the same compact size and the plug-and-play via Thunderbolt 3. Your laptop will also be charged if USB power delivery is supported.

Although the new GTX 1080 Gaming Box uses a more powerful GPU and therefore uses a larger heat sink and fan, the box itself is no louder than the original and does not run noticeably hotter. It's impressive that Gigabyte managed to build a full GTX 1080 and power supply into such a small device. It is much smaller than other eGPU cases available on the market, such as the Razer Core.

Second, and above all, we are testing with new ultraportables that use 8th generation Kaby Lake Refresh CPUs. With four cores, eight threads and a performance jump of more than 50% compared to the previous generation, there is hope that the new CPUs in these laptops will help to overcome the CPU bottleneck that originally occurred.

If you want a more detailed overview of the performance of the 8th generation U-series CPUs, read our full review.

The laptops we used for eGPU testing are the HP Specter x360 and the Razer Blade Stealth, both of which use the Core i7-8550U, the most commonly used 8th generation high-end laptop CPU.

Both have four PCIe lanes over Thunderbolt 3 – unlike other laptops with only two lanes – and both have 16 GB of RAM. The Specter x360 is configured to use the standard 15 W CPU TDP and is somewhat thermally limited, as we examined in our test of the laptop. The Razer Blade Stealth is also a 15 W laptop, but manages to achieve better clock rates in the range of 300 to 400 MHz in the steady state.

It is important to note that we tested everything with an external 1080p display connected to the GPU display outputs on the GTX 1080. The performance is noticeably reduced when the display signal is sent back to the laptop's display, and we wanted to avoid such slowdowns. We recommend anyone planning to use an external GPU to use an external display for gaming purposes. Otherwise, stuttering and performance degradation become a factor.

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