Ya if you take a small section of a screen and zoom in you can see the difference, amazing
zoom back out to normal levels and it's much harder to see the difference (when we're talking 2k vs 4k). Definitely not worth paying $600 extra for me (and that's JUST the gpu cost difference to make a game playable at 4k vs 2k)
Another **** thing I noticed is obvious issues with text if I change the res to the next lowest setting than 4k, guessing due to pixel mapping with the lower res input, but also pretty much defeats the entire purpose of getting a 4k monitor if I have to change the res between apps to make it usable.
Re the "SD to HD" that's gotta be some silly ****. 360p/480p is hugely different viewing experience from 720p or 1080p, and that's easy to back up scientifically - the average person sitting 75cm from a screen can physically differentiate up to ~110ppi.
Stretching a 480 pixel wide video over a 24 inch screen doesn't come anywhere close to 110ppi (it's 41ppi), 720p bumps that up to 61ppi and 1080p gets it to 92ppi. All still *well* within the physical range of your eyeball to tell the difference. Anyone arguing they're the same back in the day had to be on some serious baloney.
1440p on the other hand, already 122ppi
At 2160p? 186ppi
So either you're Legolas, or if you stay at an appropriate distance from the screen you literally physically can't tell whether it's using 2 pixels or 1 to display something. That's the major difference now from before; your eyes are now a bottleneck.
The best argument I do agree with is increased control over things like contrast/bleed/etc for richer visuals, but again hell not worth over half a grand for the difference it makes vs a 2k panel IMO :/ I'll be curious to run some tests when these 1440p screens arrive now