I think there might be some confusion between the LG 34UM65 and the LG 34UM95. The 34UM65 resolution is only 2560 x 1080px (27 inch montiors are normally 2560 x 1440). These pixels will be quite large on a 34" display. In my opinion, I would not spend more money than a 27" display for less pixels. Most reviewers online are excited about the 34UM95 as it has a 3880 x 1440px screen with pixel sizes that are similar to most other monitors. I am not aware of a monitor right now that has more usable space than a 34UM95, as smaller 4k monitors need dpi scaling for most people's eyes. A quick note, there is also 34UM94 which appears to be identical to the 95.
gcinfoThis post has the resolutions all wrong and therefore create an fallacious argument. please read the correction bellow.
34UM95 is 3440x1440px
34UM65 is only 2560 x 1080px