I sit about ~1.50 - 1.70m (depending on my head's position) away from a 55" Samsung TV and I couldn't tell the difference if my life depended on it. Neither could anybody who's been at my place. 4K are a complete waste of resources as far as I'm concerned and I refuse to believe that anybody could reliably tell those two resolutions apart. I feel like the 1080p → 1440p jump is substantial. 1080p looks washed out, whereas 1440p removes all the softness of the image but anything beyond that, whether 1800p or 4K, requires a splitscreen comparison to show the benefits. And I'm not even sure if that helps. Can you tell 1440p and 4K apart?