I bought used Dell with quad cpu and fhd display from ebay and chanced hybrid hdd to M.2 SSD myself. Been very happy with it although I hate Win 10 and I think I should’ve installed Win 7 on it.
I know the original thread post is old, but to anyone else with the same dilemma: Get the XPS.
An important thing that not everybody realizes about the UX501VW is that it’s basically cheating its resolution spec. It advertises 4K UHD 3840x2160, but that isn’t a complete truth. The display uses RG/BW Pentile, a deceptive trick that lets manufacturers produce a cheaper less-sharp display that they can still sell as a particular resolution. It doesn’t have 3840x2160 individual pixels that can independently express the full range of color like normal displays do, so it can’t fully reproduce a 3840x2160 picture. They look worse than the 3K 2880x1620 display they used in the UX51VZ, and the only purpose of Pentile is to deceive customers. ASUS is one of the biggest perpetrators of this problem, and their marketing of the UX501 alongside the XPS 15 is one of its most egregious cases.