27 inch 2560x1440 Monitor

I agree, it's silly to compare the Retina MBP. The big issue is the real-estate on screen. If you want the oooh-ahhh Retina you only have a 1440x900 screen. This is godawful for photo editing unless the apps you want to use support Retina.

2560x1440 is fantastic for editing. I have had a U2711 for two years and it's phenomenal. Not to mention it has a ton of great interconnects you don't find on some other monitors cough Apple cough . HDMI, 2 DVI, DisplayPort, VGA, etc...