Hi emmetbrown, Sorry for the delay, I'm using the non-curved LG 34UM95 with the Broadwell NUC5I7RYH hooked up with an MD-MD cable. The full 3440x1440 resolution is available at the monitor's 60Hz default refresh rate. My NUC5I5RYH behaves the same. The monitor will to 3440x1440 at 50Hz through the HDMI connection but I find some scrolling not to be smooth at 50Hz. This is not a NUC thing as I also have a 2012 i7quad Mini hooked to the monitor's TBolt port which also only can push 3440x1440 at 50Hz and the scrolling is also not always smooth. I switch the NUC to 2650x1440 @60Hz for some games which cannot map the ~21:9 (really 43:18) properly and the display is pixel perfect, with the extra pixels on the sides going black.
I've had zero issues with it so far in terms of usage with the NUC however I have issues with the monitor itself. The biggest is the high black level and relatively high minimum brightness. If you intend to sit very close to it, I'd heavily recommend the curved monitor as there's just a hair of darkening at the edges thanks to the steep viewing angle if you sit close. Most of the time I never notice this. I'm no fan of curved TVs but for this single person use, the curved form factor should be better.
Other notes: I'm never even once wanted more space on my screen, it surpasses everything else in this. The only other consideration is 4K Retina. I bought my NUCs for the specific purpose of 4K 60Hz support which is not available from an inexpensive Apple desktop. However I don't want full res 40" 4K as that's just too big. Rather I'd probably want ~28" Retina 4K and after having used a Retina 5K iMac recently, I just don't know if I'd like the regular rez 34" ultrawide or the Retina 28" 4K on this NUC. We shall see...