For something like gaming though, I'd assume 4K works well? Most modern games are not so text-dependent, so I'd think the text size problem would not be an issue
Well you're not going to have a problem with text SIZE when playing a game full screen on a 4k monitor.
However, what you are going to be doing is demanding a hell of a lot more processor power from your computer and graphics card to render a 4k image.
So the question you should ask yourself is are you willing to pay a real cost in performance of the game in order to have the increase in resolution. For me, 4k feels like overkill on a 27 inch monitor that is 2 feet away from my eyes. So even for games I think the trade-off is not worth it. At that distance, 2560x1440 feels like the sweet spot to me.