That update in the OP... lol...
Anyhow, yes, I'll be able to tell the difference under normal circumstances. Under your very specific update scenario, probably not 4k from 8k, but if you really want to give those goalposts legs, you may as well pose the hypothetical that if we were Daredevil, the screen isn't on, and we're out fighting crimes, can we still tell the difference? I would think this would definitely get the answer you seem to be looking for.
Look, I'm not sure what started this, but it's fine that you or anyone don't care about the resolution past a certain point, it's also fine that someone else feels otherwise. Personally, it depends on the game, I generally have lower standard if it's an anime game, or if I fully intend to play it on the go(sacrificing quality for performance is cool), but sometimes, if I'm playing a game sitting down, I really ain't going to complain that it's 4k or above, even if I was playing it at 2 metres away with a 24" screen for some bloody reason.