Level of Detail

Level of detail - and choosing texture size for images.

4k textures  of course is only for things close to the camera.

So level of detail or LOD is an important consideration and really the first stage when taking on any modeling job or designing models.

First thing you ask is will this be in foreground middle ground or back ground

Foreground of course is 4k,  middle and back 2k or even just hd would be enough.