For all these 5K widows here, read tom's hardware guide about 5K iMac..
http://www.tomshardware.com/news/apple-monitor-ultra-hd-5k-dell,27666.html
I really think Apple is getting ready to offer an 5K display... But one sourced from Sharp and only Mac Pro (or that hypothetic xMac) compatible ....
BTW the iMac will arrive this Xmas season with qHD(21") and 4K(27") displays replacing previous iMac by same price with nVidia 970/980m gpu and Haswell update cpus...
Sorry b1tches
I don't see Apple releasing two 27" Displays with seperate resolution (5k TB and a 4K iMac).