I recently started using a 4K monitor. I've generally had a positive experience and thought I would share some comments about it.
Originally the hardware was expensive and people would have to do things like using multiple cables to join their video card to their 4K screen. The latest generation of video cards and monitors don't have this problem.
I chose to use NVIDIA's entry-level Quadro K420 card, the smallest and least expensive Quadro supporting 4K. It only has 1GB video RAM and I subsequently found 1GB is not sufficient for long term stability, even for a basic desktop. The PC is a HP Z800 workstation. HP suggests they only certify the K420 with their latest workstations (e.g. Z840) but I have observed no problem using it in a Z800.
The monitor is a 32" BenQ display. After reading comments from other 4K users, I felt that any monitor less than 30" would not help me get the most from the world of 4K.
The monitor connects to the video card using a DisplayPort 1.2 cable that was in the box with the monitor.
I've been able to get sound through the monitor but I found the volume is always a bit low and at one point sound stopped completely.
Everything just appeared to work although the fonts are a bit smaller than what I'm used to. This appears to be related to DPI issues. DPI is not automatically detected and several applications have their own way of handling non-standard DPI. Discussion about this started on the debian-devel mailing list, given that non-standard DPI will be an issue with many newer monitors, handheld devices and more exotic displays such as televisions.
Some web sites just don't look so good when the browser window is maximized to 4K resolution while others use the extra space really well. For example, using the AirBNB search, the maps show more detail but using another hotel booking site I found that it was still trying to render a map within a constant size region using less than ten percent of the page.
