I like the open bed area of the 850. That was a key issue when we were shopping last year. That's "my" side of the bed and I like my feet to dangle off the end.
We have the dinette, and it's tight for two people sitting side by side, trying to eat or plan a route. We're not big people (6' 205lbs & 5'3" 125lbs). It's also a little bit of a hassle to skootch around the table in order for two to sit next to each other. If I had it to do over, with our experience of 25 nights/days in the camper since we bought it in December, I'd seriously consider the sofa. It appears to have a larger table, too, but I'm not certain about that. If I had to make the dinette into a bed every night, I'd definetly go with the sofa. The dinette cushions are sufficient padding-wise, but the 90 degree form of the seat to back is harsh. It's nice to have a little storage under the dinette, though.