I also purchased a NUC D54250WYK for the express purpose of using it with a Dell P2415Q monitor, and like bobx, was unable to get 4K resolution @ 60 Hz. Ironically, Dell itself sells this NUC (Intel Next Unit of Computing Kit D54250WYK - Barebone - UCFF - 1 x Core i5 4250U / 1.3 GHz - HD Graphics 5000 - GigE : P…), and the overview states that it comes with "DisplayPort for driving 4k displays". Now, I'm not faulting Dell for saying this--they are merely repeating what Intel itself says this NUC can do. My question is, what exactly does "driving 4k displays" mean? Does it mean just reaching 3840 x 2160, regardless of refresh rate; does it mean reaching 3840 x 2160 at 60 Hz; or does it mean something else?
Also, Intel claims its latest generation of NUCs, specifically the NUC5i5RYH, "features Intel® HD Graphics 6000 with 4K display capabilities to provide visually stunning graphics." (Mini PC Intel® NUC Kit NUC5i5RYH) I can't find any description of the precise display resolutions that are possible with this NUC; however, since it comes with a "U" processor (i5-5250U), based on the statements by Intel representatives above ("All of the current NUCs are the U series processor, which means none of them can do 4k@60hz"), the NUC5i5RYH should also be incapable of reaching 3840 x 2160 at 60 Hz. I ask those representatives, is that correct?
It looks like we 4K early adopters have been taken in by some industry hype. Whether that hype amounts to outright fraudulent advertising is a question for the lawyers. I only note that I was the victim of a similar occurrence when I bought a Sony TV many years ago that was supposed to accept 1080p input from PCs and HDMI, when in fact it couldn't. There was some kind of class action lawsuit that came out of that, for whatever that's worth.
I hope the Intel Reps can clarify what's going on here.