I'm not the most qualified to answer your questions, but out of my own experience, this is what I would say and anyone else may freely and please do correct me if I'm wrong here.
Since you have an 7700K and an 1080 Ti, I don't think there will be a CPU bottleneck. As current technology work so well with eachother that bottlenecks are hard to come by with such top of the line hardware.
Regarding the lower end cards, it all depends I would say. Right off the bat regarding better fit for you, is financially yes they will all be. They will take a significant less blow on your bank account than the 1080 Ti will, that's for sure.
Obviously they will struggle with games at 4K, as that is a very demanding resolution, even with todays GPUs.
Specially if you're planning on cranking the settings up, then even the 1080Ti might have a hard time, even though it might be capable of 4K in certain games.
With 4K, if I'm not mistaken here, you're limited to 60Hz at the moment. If you'd ask me, I would ask you why 4K? I have personally never run 4K, as I never really seen the value or point of it.
I run an 144Hz, 1440p monitor and I love it. Don't need anything more than this and it's a lot less demanding on the GPU than 4K is.
Plus, I have also seen several members on here, Dicey (Dicehunter) and maybe even Alien, being few of them, having own an 4K and being back on 1440p now. As he realized it's not "worth" it and nothing special really.
Yes, the 1080 Ti is an overkill card for 1080p and the reason they include a DVI port on the card, is for those that still hasn't upgraded to a monitor with DisplayPort yet, for example.
And another factor is multi monitor setups, where you can have an external monitor for such as Teamspeak, music etc while gaming, connected to the DVI port. Since it most likely won't require such standards of "gaming", or whatever you'd like to call it, as DisplayPort support.
Ie, 144Hz, as having 144Hz for just monitoring different programs etc isn't needed really and therefore a simple DVI port is more than adequate for the job. This is what I have done personally in the past, when I've run more than 1 monitor and run out of DisplayPort ports etc on the GPU.
Again, I'm not the most qualified regarding this. These are just my thoughts on it all and and what I think regarding your questions.
Other people here will most likely give you a better suited answer to your questions.