If it's running for up to 6 months, then probably a "summer" room. If you do go big, use the images that you like, just in case they don't sell. And large images "convey" a professional ability by the artist. I've got a 26" x 40" print over one couch and it looks good. It's a canvas, not framed. So that's not a bad size. I have another canvas over another couch, that's 40"x 60" that I made for s special show, that never sold! I wouldn't go larger,unless the designer is buying............
Rich