I'm pretty sure I would need a magnifying glass to tell the difference.
It's not about the minute detail - it's the overall quality of the entire picture. Color depth/range, compression artifacts, etc.
I can't really notice or appreciate the difference.
You need to be sitting at optimal viewing distance to get the full effect. The vast majority of people have never sat at optimal viewing distance of a UHD screen . . . because it's really, really close. For UHD with various screen widths:
40’’ TV– You should sit between 3.5 and 5 feet away from the screen.
43’’ TV– You should sit between 3.5 and 5.5 feet away from the screen.
50’’ TV– You should sit between 4 and 6.5 feet away from the screen.
55’’ TV– You should sit between 4.5 and 7 feet away from the screen.
60’’ TV– You should sit between 5 and 7.5 feet away from the screen.
65’’ TV– You should sit between 5.5 and 8 feet away from the screen.
70’’ TV– You should sit between 6 and 9 feet away from the screen.
75’’ TV– You should sit between 6.5 and 9.5 feet away from the screen.
80’’ TV– You should sit between 6.5 and 10 feet away from the screen.
85’’ TV– You should sit between 7 and 10.5 feet away from the screen.
It's noticeable at those distances, but I've found that it's super duper rare for a person to buy a 7 ft wide TV and then sit 7 ft away from it. :P