Okay, so I have chopped and changed and rung Currys multiple times to change it, but I've finally settled on the Samsung KS8000 65" (US model KS9000).
I've come and gone on this so many times, but ultimately my decision was made on brightness and sharpness with upscaling, which is *hardly* why anyone would buy such a high end TV, of course. But much of my day to day viewing is set-top box and Netflix, and non-4K games, so it is important.
The below is a very low-tech comparison of my old Samsung and this new OLED. The left side of the image is my old TV, the right side is the LG. For me, the LG looks too soft and flat despite trying all sorts of recommended picture settings (and some less recommended ones, just in case). Of course, it performs much better with native 4K content, but that still makes up only maybe 25% of my usage.
Now, there is a lot to like about this LG. I've watched some more movies on it, and things like Fight Club and Iron Man which I was testing on it last night looked sumptuous. I also looked at the punch of colours on content and was very impressed. But I just can't get on with 1. The picture processing - I'm sorry, I don't think it's as good, and I keep noticing artifacts, blocks of grey etc on the picture, even despite the fact the screen tech itself is clearly better and 2. the menu systems and remote which drive me crazy.
So I'm going for bigger, which seems a safe choice, and by all accounts the colour/contrast/blacks on the Samsung are still very good.