Upload & Sell: On
My advice would be to rent a d7100 and then compare it to your experiences with the d800. It's not a high ISO beast like the d3s, but the 24mp ought to help downplay some of the noise issues. I have and like a Sigma 120-300 f/2.8, but I'd much rather use my 70-200vr, given a choice.
With respect to the huge prints for your graduate housing lobby, I'd suggest that you're possibly being a little too critical. People used to make billboards and full page magazine shots with the d2h. I would expect that a 12mp camera could be expected to produce a decent print at the sizes you mentioned, especially if the print is in a frame, matted, with glass in front of it.
IME, the average person really doesn't care about what we photographers can see and dislike. I've printed a lot of sports posters from a 6mp camera, where the clients were just ecstatic with the results. IOW, they care much more about the content, than they do anything else. They usually don't see or care about the high ISO noise, jaggies or anything else.
Of course, these are your shots and you have to be happy. I'm just suggesting that most folks aren't likely to be as critical as you are.