Good review as usual, very difficult to portray with the conditions that were mentioned. Did I see some artifacting during the Valley 4k run?
Looks like I'll be sticking with my Dell U3011 for a bit longer. My 780ti's struggle to keep up with some games while maintaining that golden 60Hz and above refresh rate at 2560x1600. Games that ignore SLI or CF (such as the latest Wolfenstien) will have run with one GPU on a 4k screen making it even more demanding.
In my opinion 28 inches is too small for such a resolution, 30" or preferably bigger is required to really feel the benefit or desire to change. Or the need to go to Specsavers!
Tom, about the focusing of your camera on the screen - get a paper print out of some really sharp text, place it on the screen temporarily and then use the manual focus of your camera to focus on that text. Remove the paper once your happy. The problem will be if you move the camera or adjust the zoom, you'll have to focus it again...
Meant to mention - the sound in your videos is bang on