As I replied to pbacot in this thread (viewtopic.php?f=179&t=67365
) I have a Dell U3415W running off a 2014 13" MacBook Pro RD.
I was originally planning to go your route (27-28" 4K) but on researching it I was concerned about 4K compatibility issues and the impact on graphics speed with my IRIS 5100 integrated graphics, so I decided to go ultrawide and I'm really happy I did.
The huge real estate results in an equally massive increase in productivity, without the complication of a dual external monitor setup. If you're going to drive a lot more pixels (3440 x1440) might as well see a lot more on your screen - amazing to have full-size SU and LO windows side-by-side with no bezel in-between!
The .230 dot pitch / 111 DPI is higher than what I came from (dual monitor U2412M + 2007WFP) but is almost the same as a 27" QHD (2580 x1440) at .235 / 108. Menus and buttons are smaller than on my old monitor, but the plus is no visible pixelation.
Given that the U3415W is currently going for $639 on Amazon ( https://www.amazon.com/Dell-UltraSharp- ... +ultrawide
) it's a bit above your current budget: but I think the extra investment in productivity is worth it, given the amount of time we all spend staring at our screens.
The updated U3417W has a better screen with more curvature and much better speakers (2 x 9W) for $769, Both monitors include a 2 port upstream / 4 port downstream USB 3.0 hub, which also acts as a KVM for a dual computer setup. (eg laptop/desktop).
My current dream monitor is the new LG 38UC99-W 38" ultrawide monitor. It's a massive 3840 x 1600 pixels and future-proofed with USB-C / BlueTooth.... but costs $1500
. The entire LG 21:9 ultrawide series plays nicer with Mac OS than Dell does — which isn't a consideration for you, but is for me. There's tons of model choices — with a broad range of quality/features/price. ( http://www.lg.com/us/ultrawide-monitors
Sorry for the long post, hope it's of some value.