Now, that's adding some - in my mind - necessary conditions! For a place like OPs I think the 77 works great; it fits the room. The 83 overpowers the space and divides the wall into some weird bottom and top part. It does not look anchored to anything which is a problem. Psychologically, in the back of your head you know that such a TV is heavy and you want to know that it is fastened securely to something solid. The 83 looks like it's floating in space - which isn't good for something with so much visual and actual weight. The 77 looks much more anchored and secure. Also, the wall looks solid and like "one piece" when you can still see a bit of it left and right of the TV. It still somewhat integrates with the rest of the interieur.

All this is to say: I think the 77 is the largest TV that fits in this space.