No i am using 1920x1080, 4K feels too small detailed or too big sized for me.
I think my slow downs caused by CPU, or may be model/particle loading to GPU, but not a drawing on screen.
I remember slowdown even when i see bare wall without and structure behind. Show electro and flying lightnings and escaping or detonating dynamite. (But dynamite not slowdown itself, +1 to gibs/physics checks)
I playing with some random video settings only at beginning, and see no difference. My general settings fullHD+fixed60FPS+vsync+max-antialising+max-textures.