I think most people would go for the bigger TV. There are advantages to the B1 over the Q80A though such as better screen uniformity, better viewing angles, perfect blacks and no motion blur.
There's not enough between the two TVs to be worth downsizing in my opinion. Perhaps a better option if you wanted OLED tech would be to go for the LG A1. You'll get more motion blur, but it should be an OLED TV available at 65" for cheaper than the B1.
There are also other OLED TVs, including models from last year that you may have local availability of. In the UK the Philips OLED706 tends to be a good deal.