I have a Seiki 39in that I use as a second monitor for my rMBP - the PPI (110) is the same as the Apple 27in Thunderbolt and they have roughly the same picture quality once you calibrate the Seiki. 39 Inches of uninterrupted space is awesome the only downside I've noticed is some mouse lag under OSX which can be fixed with some quartz settings that then cause screen tearing, I've read it's not present under windows so maybe it's something that can be worked out with a software fix.