First time ever from me - 4K benchmaks! All the details about my testing methodology and video cards you can find in techpowerup forums.
Those who prefer video viewing instead of reading open 4K gaming benchmarks: RX Vega 56 OC vs. GTX980 Ti Strix OC vs. GTX1070 Strix OC vs. GTX1080 SC video to see the results straight away!