Seem ok to me mate. Take the results for The division as an example for both cards overclocked.
1080ti - 58.9
980ti - 33.7
58.9/33.7= 1.747
174% which is what the graph has it as. I also tried a few other games and it worked out.
Hover your mouse over the 980Ti overclocked results for the percentages to pop up, this is on the second graph.
Its my maths lol. I got confused when i took 980Ti performance 33.7 dividided it by 1080Ti performance because i wanted to know how much faster it was.
33.7/58.9 then multiplied it by 100 to get 57.21% faster. So i was like mehhh? Then started trying to work out 10% after that haha.
i always got confused working out percentages.