I run a Dell 31.5" 4k and find it a perfect fit with the rMBP running at the (effective) 1920x1200 resolution. The Dell runs around 140ppi and the effective ppi

I run a Dell 31.5" 4k and find it a perfect fit with the rMBP running at the (effective) 1920x1200 resolution. The Dell runs around 140ppi and the effective ppi of the rMBP is around 140 also. I find it to be an excellent combination. The quality of the Dell is outstanding. 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.