I don't think it ever made sense to say it's generally hard to tell 4K from 1080p. It just really depends on the viewing distance and size of the screen.
My tiny laptop screen is almost 4K, and the difference is massive from a 1080p screen because I'm so close.
Likewise, your 55" inch screen wouldn't need to be 4K if you sit 10 meters away from it.
Well, as I think I may have said poorly, I don't really know if I can tell 4K from 1080p reliably, because a 4K stream that contains such high quality pixels in it that it qualitatively different than an upscaled 1080p stream is very hard to come by right now.
According to the charts, I'm right on the outer edge of where it may make a difference, so it's at least physically possible I could tell, if I got a truly 4K stream.
My tiny laptop screen is almost 4K, and the difference is massive from a 1080p screen because I'm so close.
Likewise, your 55" inch screen wouldn't need to be 4K if you sit 10 meters away from it.