If the Display is from Samsung I am out. I have had multiple AMOLED Displays from Samsung burn in on me... Its never been a problem with my 3 prior Xperias with 4K Display (XZ Premium LCD, X1 II OLED, X1 IV OLED) likely because Sony could tune them how they pleased and set the max. brightness timidly.
I also have qualms with the change of resolution. I have good enough eyes, where I can see single pixels on 6"+ 2K displays from time to time, maybe is just how i use my phone, when watching content in Bed, but its never been a problem with 4K displays.