I also went from 980ti to 1080ti and I'm pleased with the improvements. (Both are the Zotac Amp Extreme)
Even with overclocking one of the fastest cards money can buy, I can't get 90 fps AND crystal clear graphics in all game situations, so set your expectations accordingly.
I prioritize graphics quality over frame-rate. My frame rates are 90 in space, 75-90 in rings, 45-60 on planet surfaces, and 45 in stations.
My setting on the 980ti were 1.5 in the debug tool, 2.0 HMD in game and x0.5 SS. Shadow/material/texture qualities were low.
With the 1080ti I can use 2.0 in the debug tool, 2.0 HMD in game and x0.5 SS. All quality settings are high or ultra.
But as I mentioned, I have an overclocked high-end 1080ti. Your results may vary.