CPU aside, the Zenbook UX501 may not be what you want, because it uses a PenTile (RG/BW) not-true-4K display. The RGB in each pixel is replaced with either only RG or only BW. This means you get all the performance requirements and risk for content scaling issues of 4K, without the full sharpness of 4K to even show for it. ASUS does this on just about all their current high-res offerings, and it's commonly regarded to be a deceptive marketing practice. See the sidebar on /r/SuggestALaptop/ for more info.

What you might want is the Dell XPS 15. You can get it new or you can get great deals on refurbs in the Dell Outlet. And the build quality is so good it doesn't matter.