@Wetrix 2160p is just 4k, they're the same resolution just listed differently.
There's a lot below and while its still simplified, the TLDR is, 4k is awesome but certainly not as good as it seems in stores.
I have two 1080p monitors, one 4k monitor, and two 4k TVs, I see an insane difference on the TVs compared to 1080p like it's a little crazy the first time you see it, but not so much on the monitors due to the smaller screen.
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