Cheers for the reply. Good points. The iMac 5K here at work is awesome and probably all the power I need. I don't do much with video, just coding and some image work (Sketch, Photoshop).
Having seen the Dell UP2715K screen, I don't think it's the best looking. Total cost of the card + screen is about the same money as a ~6 month old iMac 5K. Another issue is I use a Bretford Mobile Pro to mount two 27" and the iMac 5K has to be specially ordered in VESA mount ?!?. I think I'll wait for now then. Damn.
Well, look at it this way. The two 27" ACDs at home will remind you you're not at work.
I actually run 'dark menu & dock' at home so when I'm home I feel like I'm not at work. When I'm in the store and look at the Retina iMac and look at a ATD, the difference is stark side by side...so I guess I can sympathize. I've got 2 Thunderbolt displays at work and 2 cinema displays at home, so on a daily basis I'm not exposed to anything different. I don't know, it's really all preference. Look at it this way, a lot of the world still uses little cheap 23 inch Dell monitors. The apple displays (ACD, ATD) are still a sexy resolution and are ascetically appealing. I've got a hardware calibrator that keeps my colors in check, and I make sure to keep distance guidelines in check, so I don't see pixels anyway. I think these monitors are big, bright and pretty darn cool.
Here's why I will hang on to my ACD's for a long time...The discontinued cinema display will outlive it's successor (ATD) as USB-C/displayport alternate mode starts to become more common. Theoretically, with a simple adapter, the 27 ACD should continue to operate as expected. Just like now, the cinema display is usable on any PC with a display port connection. The same has not been said for the ATD. The display port signal in the thunderbolt display, to date, has been impossible to parse, so I doubt an adapter will ever be created unless Apple has some kind of adapter up their sleeve for Thunderbolt 3, which I'm sure would destroy sales if they truly are intending to unveil a "Retina Thunderbolt Display" at some point in the near future.
On the flip of all that useless information, have you considered a 4k display with your current setup?