Brilliant haha

I had a 40" 4K TV as a monitor for like a year. I was sitting close, but you could definitely see the resolution quality. It looked very similar to the pixel density on a 27" 1440p, just bigger. I don't know where the cut-off is, and it may be different for different people. IMO 27" 4K is probably a waste but maybe 32" would be noticeable. 40" was.