Happy to expand: As I said, I got my UHD430 yesterday, less than 48 hours after ordering from a accessorieswhole on ebay for $759. I was a little worried about dead pixels and the difficulty of returns in that case, but there was no issue.
The only hiccup on installation was that the monitor would very quickly go into power-saving mode if none of the default inputs (which did not include the displayport) had any signal, so I had to scramble on the Korean remote to make DP the default source. No problem once that was done.
Image-quality is substantially better than on my old Seiki 4K and nearly as good as on my old Dell 30" reference monitor.
Running some simple tests show that the monitor definitely does 60 Hz at 4k. It can be cajoled into accepting up to 240 Hz at 1080p, but after some preliminary tests, I am not sure that it actually displays at a higher rate than 60 Hz at any resolution. Needs more investigation.
The front of the monitor is very nice looking with a relatively thin metallic bezel; the back is a less attractive plastic, but then you don't see that.
The monitor position is not adjustable, which I think may become a problem for me. Fortunately it has VESA holes and is surprisingly light, so an articulating arm should fix that issue relatively easily.
As for monitor size, this is a subjective issue. My subjective experience for over 30 years has been that my productivity and comfort increases substantially with monitor size. My 50" 4K Seiki was the first time in my life that I felt that my monitor was actually too large; seeing all of it required movement of the head and not just the eyes. On the other hand, going back to the 30" Dell (after the Seiki died) was a much worse, almost unbearably cramped experience.
So I think that for me, mostly working in many windows simultaneously and playing the occasional not terribly FPS bound game, the sweet spot is probably in the 40-43" range. If I played a lot of FPS-heavy games, I might chose a smaller monitor with a somewhat lower resolution.