I like 4K (3840x2160) because it perfectly upscales 1080p (1:2) and 720p (1:3). But it's still a lot of pixels to push for refresh, so anything but a TN panel usually has ghosting on the low-end.
I would never, ever recommend 4K for Windows usage, as Windows and its applications is still stuck in the '90s using too many bitmapped graphics. They don't use heavy vector graphics and scale like MacOS X and Linux applications have since '01 and '03, respectively. But if you get a large enough 4K for Windows, say at least 37", you might be okay.
I end up running my 28" 4K in 1080p on Windows, or an imperfect 1440p, when gaming. With Linux, using a 200ppi scaling and it looks beautiful. Even low-end LXDE (Openbox) looks just fine as it's all native GTK+, and I don't have to run a compositing desktop environment like GNOME Shell or KDE Plasma. Everyone comes in and says, "Can you make my computer look like that? I also like the classic Windows 95 bar too!" Where do I begin?