I upgraded from a 980 ti to 1080 ti early this month. I ran some benchmarks before and after the upgrade. I mainly focused on 3440x1440 though I included 1440p for some of the benchmarks.
The 980 ti benchmarks were ran using driver 378.92. The 1080 ti was under driver 381.65. All tests were ran before the recent windows 10 creators update. All benchmarks were ran using the same settings on both cards. All benchmarks are ran using built in benchmarks.
For settings I marked if I used a preset. If no preset was available I instead screen shot the settings used from Geforce Experience.