We begin with the test result of the 3DMark benchmarks.
The GeForce GTX 1080 Ti's overall score is about 25% higher than the GeForce GTX 1080's in the "Time Spy" test under DirectX 12 at a resolution of 2,560 x 1,440 pixels. The Graphics Score controbuted significantly to the 1080 Ti's overall score - the card had a 32% lead over the GTX 1080.
In the "Fire Strike" DirectX 11 benchmark, both the "Ultra" (3,840 x 2,160) and "Extreme" (2,560 x 1,440) results gave the GTX 1080 Ti a 30% lead in the overall score, over the GTX 1080.
In the Fire Strike test under Full HD resolution (1,920 x 1,080), the difference in total score of the 1080 and 10880Ti GPUs was reduced to about 16%, and obviously the CPU acts as a bottleneck here.
In "Sky Diver" and "Cloud Gate" becnhmarks, which pose a lower load to the GPUs comapred to the Fire Strike becnhmark, the score difference between the 1080s was further reduced at about 9% in Sky Diver, with both GPUs to perform equally in the Cloud Gate test.