Interesting! We have the same CPU, so hopefully that
should eliminate any variance and make it a straight comparison of GPUs.
I scored 60.1 FPS and 1515 in Unigine and 51.0 FPS and 2135 in Valley using the same presets as you. That makes the 1080 Ti 27.6% faster in Heaven and 12.9% faster in Valley.
I guess the caveats there are that the Unigine benchmarks run on OpenGL which are always going to look bad compared to Metal or DirectX in Windows.
I did a run of GFXBench Metal too, which is free from the App Store and the results are below - ignore the 'onscreen' tests as these are run at native resolution, which for me is 3840x1600.
For clarity, my cMP is a W3690, 32GB RAM, GTX 980 Ti 6GB FE, 525GB 2.5" SSD.