There is no such resolution as "3K". Back a couple years ago MSI released a laptop with a 2880 x 1620 resolution it called 3K, though any panel with around 3000 lines of resolution could be called "3K" as a marketing gimmick the same way "4K" panels now are UHD and not actually 4K. Anyway, I see 3200x1800 on there, so why isn't that "3K"?
Seems like you don't understand what's going on.
There are two monitors on screenshots. Top one(1) is 16:10 with resolution 1920x1200. You can't set 3200x1800 VSR on it.
Bottom one(2) is 16:9 with resolution 1920x1080, and you can set 3200x1800 VSR on it.
Videocard is 290x.
Finally I can downsample slightly more than 2k, but I can't do it on 16:10 monitor. Why?
We need option of 2560x1440 and 3200x1800 resolutions on 16:10 monitor too.