Sorry, but this benchmark isn't very helpful from my experience. Even a single 1070 can maintain 60 fps at 3840x2160 just by lowering shadows, ambient occlusion, and vegetation. The end result is a very mild reduction in image quality.
At max settings minus AA, my 1070 pulls about 30 fps, pretty close to the results.
Ambient occlusion and shadows are the big killer in this game and you can turn both off. Disabling shadows makes the game look bad, but even a 1070 can do medium shadows easily. I bet a 1080 can eek by with high, but ambient occlusion must remain off.
I must say, ultra shadows + hbao really looks nice, but it nets in a huge performance loss.