I was going to suggest a smaller size so that you can spend a little extra on better features BUT, as you say, you have a large room hence need the size. So... considering your budget and the fact you are looking for an upgrade then I would look at the Hisense H55N6800 that
@Gavin. mentions above. It's a pretty solid panel overall and well-priced at the moment. It's not the best for gaming as it has a relatively high input lag (some 32ms+) but it's probably not noticeable / an issue unless you play competitively and need ultra fast twitch reactions. It also does a half-decent job of minimising motion blur in fast-paced scenes. You will need to switch it into the 'gaming' mode though otherwise input lag will be even worse in 'normal' modes.
Also, it's not a true HDR (high dynamic range) as it uses an 8-bit panel and FRC. In a nutshell it doesn't have the colour range of higher priced sets nor can it deliver true colour accuracy due to the lack of precision compared to 10-bit sets. It uses FRC to 'fake' colour representation (by quickly flicking between two colours to fake the eye into seeing an intermediate colour between the two flicked-between colours) but this is not something you'll probably care about given your circumstances and upgrade needs!
The HDR is a fancy way of saying the tv can display an extended range of brightness values from dark to intense bright colours. However, as said, this is not a 'true' HDR so you won't be able to see truly intense brightness as the output is quite low in terms of peak values. That said, it will be fine for standard stuff so it's not something I'd worry about in this case. It's a solid 4K set and you won't get much better at the price to be fair (not at the moment at least).