AMDMatt did some BF1 videos @ 4k on his Vega64 AIO and was averaging around 65fps at I think max details.
Hopefully he can pop in here to clarify.
But as a PC gamer, I feel that 60 is the absolute minimum and as such I will buy (monies permitting) a 1440p Curved UW as I think that will give a better long term experience.
100fps (or near that) on titles now at max settings I would hope be achieveable, so when upgrade time comes around again in 3-4 years I'll be hitting 60fps or lower at 1440p.
I'm sure the 1080ti gives better frames in most titles @4k, but not by enough to justify buying it for 4k as I don't think the longevity is there for it or any card at 4k right now.
I did a similar thing 3-4 years ago, bought a ROG Swift GSync 1440p and my GTX770 was man enough to power my current titles around 60fps - some higher, but gsync here helped (aside from the flickering).
Fast forward to now there are just some games I cannot play @1440p - dropping res is unacceptable and these games don't even play 30fps on lowest settings (ARK, I'm looking at you). So yeah, not making the same mistake this time around!