Do you already have the UX501 or are you intending on purchasing it?
If you are intending on purchasing it, and are looking at a model advertised as having 4K 3840x2160 resolution, know that it is using a false-resolution Pentile display that can't actually display the full 4K resolution, and creates a grainy appearance as it downsamples that resolution onto its incomplete dot array.
The Dell XPS 15 4K and Lenovo Y700 4K have true 4K displays, I would consider them first.