While I'm sure it's great to have such massive screen real estate (I wanna get a 4K in 2014 too), I can't but help think this is the programmer equivalent of consumers buying needlessly large TVs.
I work on a 24" desktop monitor and a 14" laptop one. How is 50" the "ideal size"? Even 39"? At what point does the law of diminishing returns kick in? Sure, it's great to gave 7 windows side-by-side, but is it that much of a productivity jump from, say, 4 windows or 5 windows?
Personally and subjectively, I'd draw the line somewhere around the 28-32" screen size.
To sum up, the core argument here seems to be that upgrading to a 39" or 50" monitor is great because (a) it's cheap, and (b) more is always and infinitely better.