Games I play such as insurgency sandstorm I can easily average 120fps.
Some settings that munch GPU such as Blur and post processing I don't like anyway. Only require light AA at 4k if any. Many setting syou can barely notice any difference unless you sit and look for it, such as shadows. So maybe on slower paced games such as Witcher 3 you may want to up it, but even then the mods for detail enhanced 4k with not much GPU processing requirements.
At 4k you wouldn't put AA to max but many reviews and benches to make them standardised is put everything on ultra and gives low fps as a measure. But the fact is that the options in the games aren't there to just put to max otherwise there would just be a low, med, high and ultra setting and that's it. All the options are there to tweak and play with to get a decent image with high fps. So many will say that you cant get 4k at over 60fps....welll you cant iff you turn everything on and to the max, but they don't put all those options in the gfx menus so you cant play about with getting a decent image with high fps.
So on many games I'm looking at 90-100fps so a 120hz 4k will do me well. I'll be looking at the next gen gfx cards for a purchase as the 2080ti didn't give enough performance for the extra money. No doubt the 3080ti will be an arm AND a leg but we'll see. Also with OLED - whilst it's definitely much better image quality I'm wary of spending 100's if not 1,000's more over tech that will be much cheaper and common place in a years time. With my TV I couldnt stomach paying 1,000's more for blacker blacks when everything will be OLED or equivalent soon enough.
Hence why £900 is still a bit steep for an IPS/VA on these current 4k 144hz monitors and I havent yet parted with my cash. I am looking though.