Synthetic benchmarks might not offer definitive proof on how the new flagship GPUs from Nvdia perform versus the previous gen, and the drivers used are most likely not final either, so performance could slightly improve upon release. Additionally, since the official Turing drivers are not yet publicly available, these results seem to be provided by an Nvidia or AIB partner employee.
https://www.notebookcheck.net/Nvidia-RTX-2080-Ti-is-only-35-faster-than-the-GTX-1080-Ti-in-preliminary-leaked-benchmarks.328680.0.html