I think subject matter might have some input on print size too. A portrait or shot of a small object or an abstract view of some scene might work well as a relatively small print, especially if it's a fairly simple composition without lots of little details. Grand landscapes and some architectural subjects sometimes beg for a large presentation. A philosophical question perhaps of whether we want the viewer to look at the picture or to feel almost "inside" the picture.
All that said, I'm not currently equipped to go more than 11x14, so that's it for me. Of late I do mostly square format, printed on 11x11 paper (using the offcut for test strips!) and mat it to about 10 1/4 square. Optically centered and double matted in a vertical 16x20 frame it makes a nice presentation. Folks don't often reach for their wallets, but I attribute that to my bent toward industrial archeology as subjects!