A co-worker got two of the Dell 28" 4Ks and they were too small for 1:1 and just a waste for 1920x1080. Anything in between was jagged. The 30Hz was pretty terrible also.
Maybe two 24" displays would be ok, but I'd rather have the extra pixel real-estate in a single display instead of smoother font and graphic rendering.
The only option seems to be the Auria eq278c[1] and eq308c[2], both resolutions are 2880x1620. But since it came out less than 1-2 months, there isn't any reviews for it yet. Its cheaper eq $400 eq276wn claims to be 2880x1620, but reviews says it's actually a 2650x1600, so I'm not going to plunge $750-$1k until there's a good reliable review for it. The other alternative is the new LG 3440 x 1440 [3], but it's not as ideal as 2880x1620 since it requires a bit more head tilting since it's much wider and harder to do 2 vertical windows editing at 1440 vertical pixels.
1. http://www.amazon.com/dp/B00KG5LWM4 - eq278c, 27"@2880x1620 = 122ppi, $750
2. http://www.amazon.com/AURIA-EQ308C-30-2880-1620/dp/B00KG5LSB... - eq308c, 30"@2880x1620 = 110ppi, $1055
3. http://www.amazon.com/gp/product/B00JR6GCZA - LG 34UM95, 34"@3440x1440 = 110ppi, $999
I run my 13" rMBP at 1440X900, which still looks pretty good. It actually looks pretty good at 1680x1050, except that everything is too small for comfortable work. Sure, it wouldn't be "full retina" resolution, but it would look a lot sharper than a regular 27" 1440p display. The only real constraint could be the video chip's ability to render at 2X that resolution and then downscale.
Support on Windows and in games is spotty though. In particular, Windows doesn't seem to have a way to do exact pixel doubling.
Now to wait until all my core windows apps are either 4k native, or scaling compatible.
Are there any themes that help with that?
Reposting from my comment last year:
At 28", a 3840 x 2160 panel has a PPI of 157, which sits right between Retina and non-Retina densities. This means that on a Mac, you’ll have to use it one of two ways: Either at 1x, where the higher PPI means everything will be much smaller than it is on a normal monitor, or at 2x, where the lower PPI means everything will be much bigger than normal.
...
The best 4K monitor for Macs will be a 24”, which will have a PPI of 184, just about right for something sitting a bit further back from the viewer than a 220 PPI Retina Macbook Pro display.