I decided to get a 85" Samsung for my bright family room environment. I have a projector in the basement. I must say that I don't think the 77" was available (or affordable) when I went to the 85" TV. I moved from a not as bright plasma to the LCD, and it was certainly a tradeoff.
If you've done your homework, then you know that there is a tradeoff. You don't just get more size, you get more brightness. FAR more brightness! This is horrible on the black floor, but phenomenal for daytime viewing in a bright room. When we watch at night, we used to always keep the lights off, but now we usually have some lights on. The image isn't great at night. Well, at least the black levels aren't what we got from our prior plasma. So, I know OLED would be a significant improvement in that regard. But, the brightness and size have been quite enjoyable for the five+ years (or so) that we have had it.
Yes, the 83" OLED is in a different price class, for some reason, than their 77" model. Not worth it for 6 inches.
The 85" is worth it and looks great, but won't give you those amazing inky blacks. It will destroy on brightness though.
If you have reflections and windows behind the seating position, I would definitely go with the 85" LCD. If it is just light from the sides, it would make it a much more difficult decision.
Nobody really can decide for you.
