I have yet to have anyone complain about too large of a TV and I constantly talk up to a larger size. Half the time I'm not even selling them the TV, I'm just hanging it.
We sit about 12' from an 85" TV, and if we could get a reasonably priced 98" TV, I would've used that instead. There is no fatigue, and a 1.5x viewing distance to the WIDTH is considered common. In reality, 10" to 12" of diagonal is comfortable for most viewers for each foot of viewing distance. So, yes, from 8' viewing distance (eyes to screen), having a 75" to 85" diagonal would actually be quite comfortable for most viewers. 65" is no problem at all. Be very aware of your eyes to screen distance, not the couch to screen distance. Also, try moving the couch a couple of feet closer for a day or two. See how you like the screen size. Sitting about 6' viewing distance for a 55" would be similar to sitting 8' away from a 75" screen.
Thanks for the feedback. I guess there is a little more to the issue than just size that I'm thinking about. My current set is 51 inches. Relative to the wall and space I feel like it looks reasonable.
A 55 inch OLED is about 1 1/2 inches wider and about the same height (not including the stand) as the 51 inch with the bezels so it would look similar. A 65 inch would add about another 9 inches in width which, if mounted on the wall, would need to go all to the left side due to the light switch on the right. I'm not sure, but I think it might look a bit off balance (I cut out a piece of cardboard to check out the size, but I'm still not sure -- cardboard is not the same as a picture).
Also, at the moment the very bottom of the screen is covered ever so slightly by the center channel speaker. A new TV would not be able to sit on its stand because there is no bezel like there is on the current one. If I have the set wall-mounted it would push it back probably about 8-10 inches after leaving some room for the mounting hardware,. which argues in favor of a larger set based on viewing distance, but it will also raise the TV.
The stand is about 24 inches high and the center channel is about 6 1/2 inches high, so if the TV were mounted a couple of inches above that, the top of a 65 inch set would be around 65 inches up the wall (approximately 32 plus an additional 33 inches height for the TV). The center of the set would be about 16 1/2 inches lower or around 48.5 inches. My couch/sofa is a little low so I figure my eyes would probably be at around 40 inches or a little lower when sitting. Does that seem about right? I'm afraid I might have to look up too much while viewing.
Perhaps I'm overthinking it.