A 65" TV is just about right for my viewing space. I could go 75", but I think it would look funny. I was an idiot for not getting a 65" two years ago when I got my 55". It was only like a $500 price difference on the Q7 QLEDs (Samsung).
On the other hand, if I go through with doing what I want to do with my bonus room, it makes it easier to justify getting a 65" now for the living room.
I will say that one thing I like is that most TVs are now going back to a centered stand. Those end legs are fine on smaller TVs, but end legs on a 65" would barely fit my TV cabinet. I couldn't even put a 75" with end legs on it, which would mean getting a whole new stand - probably one of the newer ones that have the watchyamacallit mounts on them, like a wall mount. I really like the TV stands that have those as well.