I received both my Mac Mini and the 43" LG today. I'm using it as I'm typing this connected to the 43" LG in full 4K 1:1 pixel mapping mode. My daughter is watching Netflix on the bottom left corner, I have slack going on top left corner, and 2 Safari windows on the right side.
I'm absolutely loving this. The wow factor has won me over and I'm not missing the iMac's 27" display anymore. I'm sitting about 2.5 feet (76 cm) away from it. Interestingly, I find myself wishing that the text was slightly bigger at the default zoom level. So I'm thinking I wouldn't mind going with a slightly larger screen.
And oh, the Mac Mini is great, too
No stutter whatsoever with the iGPU and I'm very happy that I sold my 27" iMac. This is worth the experience.