In the recent past I have had: GTX 980ti, 1070 (desktop and mobile), 1060, 1080ti and RTX 2080ti.
I actually used to run ATI and Nvidia side-by-side, but the last ATI, an R290X, screamed into oblivion using 250 Watts at THD.
Monitors were 1920x1200, 1920x1080 and then came 4k...
To make a long story short: Everything below the RTX 2080ti disappointed. Plenty of the cards advertised 4k, all of them could do 2D at 4K (and so can various Atoms, even my $99 Jetson Nano, albeit at 30FPS), but when it comes to moving gaming from 1920x1080 to 4k, only the RTX 2080ti delivered in full.
What I mean by "in full":
The GTX 980ti turned out to be pretty much the exact same performance as the GTX 1070... at half the power consumption. But even the GTX 1060, a slightly overclocked but completely "overcooled" MSI (actually phyiscally bigger than even the RTX2080ti, but has the unique advantage of being "unheard") can do 1920x1080 at ultra settings in every game I've ever run.
So all these intermediate GPUs, above the (good) GTX1060 (which performs at a very similar level as a "bad"/mini 1070) are fine-to-overkill for that standard THD resolution at any quality setting.
Just like they all, including the GTX 1080ti, which I specifically bought in preparation for the 4k upgrade, fail, when you quadruple the graphics workload. Unfortunately that's exactly what happens when you go to 4k: Four times as many pixels.
The pain I felt with the newly purchased GTX 1080ti on the even newer 43" 4K screen after launching my favorite game, is something that I won't forget. I didn't matter that it performed just fine at 3K... At 43" you can see the difference!
So from that point on, unless you go with the RTX 2080ti (or better), you'll have to tune and compromise. There will be games, that work with a 1070, a 1080, 2060 or whatnot even at 4k. There will be settings that will get these games to work at 4k or you can leave everything at epic/ultra but reduce the resolution. If you are happy to try or your 4k monitor is really too small to show the difference, you may be satisfied.
I replaced various 24" monitors with a single 43" screen and I sit close enough to tell the difference. Unfortunately I also happened to play ARK Survival Evolved, which just loves to eat hardware, much more than many other titles I tried.
So I went and bought the big beast, tax deductible because it use it for machine learning. It may be outrageously priced, a beast, unfair or whatever. But it does deliver on 4k what the 1060 delivered at THD: Acceptable performance without tuning those settings.
I then rotated all these other GPUs among the many members of my family and made them all happier.
That screen is practially guaranteed to be the cheapest part of 4K you purchased.
Remember that when 8K comes around...