If anything posting this survey just shows little OP (and the folks over at ResetEra) understands about basic PC terminology. Primary Display Resolution is your Windows Display resolution.
There is a reason why not many people have their Windows display at 4k. I'll show it in a picture.
There. See that lovely Windows 10 (I hate it, 7 for lyfe) GUI on a 4k resolution? Can barely read the text. It's worthless. While yes, there are ways to make the display 'normalized' it's much easier to just set it to 1080p since it's so much easier on the eyes. Hope y'all console folk learned something!
On any windows 10 PC i've used, the resolution is set to max by default and it uses screen scaling to make things the correct size (also by default). I don't see why you would want to use native 1080p when you have a 4k display. I just checked and even though scaling makes everything the same size, icons and fonts look blurry by comparison. Easier on the eyes it is not.