CPU and Storage Performance
The Core i7-8705G falls into a strange place in Intel's current mobile CPU lineup. Kaby Lake-G is sandwiched between the 15W quad-core U-series processors and the 45W six core H-series CPUs. As a result, we are comparing the XPS 15 2-in-1 to a variety of 8th generation U-series equipped notebooks, the Ryzen 5 2500U, and the Core i7-8809G found in the Intel Hades Canyon NUC.
In Cinebench R15, the Dell XPS 15 2-in-1 manages to slightly beat our previous performance winner in mobile testing, the XPS 13 9370.
Additionally, there is a significant performance gap of over 15% between the Kaby Lake-G powered Hades Canyon NUC and the XPS 15 2-in-1.
Handbrake shows a 10% encode time advantage for the XPS 15 2-in-1 over the XPS 13 9370 but falls 15% short of the encoding speed of the Hades Canyon NUC.
Charting the CPU frequency during the Handbrake encode points out an interesting dynamic of the XPS 15 2-in-1. The clock speed seems to be ramping up and down in a sawtooth-like pattern to prevent thermal issues.
Looking at the Processor Power data from this same encode, we see the same sawtooth pattern as the processor hits the 50W maximum TDP, and then downclocks, only to start the pattern all over again.
Regardless, the average clock speed of around 3.2 GHz provides a significant advantage over the Kaby Lake Refresh-based XPS 13 9370.
PCMark 10 Extended is a benchmarking suite that aims to emulate several different usage scenarios ranging from basic productivity to mixed workloads, as well as light gaming and to applications for creative professionals like photo and video editing.
The AMD Vega-powered graphics of the Dell XPS 15 2-in-1 allow it to slightly outperforming the GTX 1050-equipped Surface Book 2. However, in the more CPU-bound Essentials test, the XPS 13 9370 manages to pull an over 5% lead.
Overall, the CPU performance of the i7-8705G seems to be much closer to the 15W Kaby Lake Refresh quad-core CPUs than we would have expected. Despite sharing a CPU architecture (Kaby Lake), and having an extra 30W of power draw in the Dell XPS 15 2-in-1 design, the performance benefits don't seem to scale on purely CPU-bound tasks.
Storage performance has been disappointing with the last few notebooks we have looked at recently. Both the Microsoft Surface Book 2 and the Dell XPS 13 9370 seem to be employing write speed throttling, artificially limiting their high-end SSDs to sometimes embarrassing rates in the name of power consumption.
SSD speeds aren't a concern with the XPS 15 2-in-1 though. The SK Hynix PC401 SSD provides over 1.0 GB/s sequential write speeds, and over 2.5 GB/s sequential read speeds.
While not the absolute peak of modern NVMe performance, the 1.0 GB/s write speeds are suitable for notebook applications where it's difficult to generate the data fast enough to saturate the SSD in the first place.