I recently added an Asus PB287Q 4K monitor to my setup. Whilst a TN panel it is a truly excellent example of one. Running under Ubuntu 15.04 with an MSI GTX 960 Twin Frozr 4GB is a really nice experience – sure you have to play around with scaling to make sure you can read the text, but that is pretty trivial to sort out. And it is so much better than Windows under the same circumstances.
Note: I have yet to try Windows 10 on a 4K monitor – I am hopeful some of the scaling issues have been resolved. If not, I’ll run it in a VM 🙂