Yes I am a 1080p max settings user, with my GTX 980. Note my monitor is only 22" (or 21.5").
I read an article about high vs ulta settings. The reviewer said they couldn't see any difference, compared to the performance drop. However I have not tried this recently. The last time I tried it was probably Crysis and the difference was obvious.
One game that I know the GTX 980 won't do max at 1080p, is Rise of the Tomb Raider. The Witcher 3 will not either. I recall even Fallout 4 won't. There are quite a lot of games, and new stuff like Shadow of War won't. The 980 won't have enough vRAM to run SoW max probably.
I am going to have a think about this idea of lower settings. However I played The Witcher 3 on max and loved it. I even ran it at 1440p DSR maxed out for sometimes.
There are some max settings that I think are important though. (Am thinking of Yuka's list.)
1. I found HBAO made all the difference in Fallout 4, compared to the lesser setting. It made F4 look more alive.
2. I like either to push to 1440p DSR or run anti-aliasing. I usually opt for FXAA. Some games just need more aggressive anti-aliasing at 1080p though. I find this important because it takes the sparkle off. E.g if you go to a town in The Witcher 3. Then look at 1080p with whatever TW3 uses for lower AA. Then switch to 1440p, the difference if clear. Alaising on characters is gone, and they don't sparkle as they move. They seem more colourful too. ...... While this is 1440p though, so for the same effect at 1080p. TW3 @ 1080p with max settings, and high AA, it's going to struggle a bit.
Therefor even at 1080p yes I think GTX 980 is getting a bit old. It does very well though and most games it keeps near to or constant 60fps. For games like Rise of the Tomb Raider, well simply I have not bought that yet. Firstly because I will wait for a sale, and secondly I may wait until I have a more powerful card.