Hi,
John Lewis and Richer Sounds sell both those Samsung models. I suggest you book an appointment for a side-by-side demo with your local RS, say would they connect a 4k player so both TVs can share it, and take along a blu-ray/4k blu-ray/other sources you might watch, and demo the TVs.
My tip is ask them when the shop is quiet and go then. RS in Liverpool were very helpful and had the TVs set up for me with a blu-ray player, offered me coffee, couldn't do enough for me, and I didn't even buy a TV the second time.
I couldn't make an appointment with JL so don't think they do appointments any more but you could go along and see the TVs. When I went along to Liverpool on the off-chance early one morning the salesman attempted to connect the TV to a blu-ray player but my blu-ray wouldn't play.
He said my blu-ray was faulty and I said it wasn't. There was another player connected to a different TV so he tried that and it worked, but he wouldn't move the working player to the TV I wanted to demo.