16x20 was the size I use to print, with a 20x24 here or there -- but now all contact alt processes (up to 11x14).
We have a mural assignment our intermediate class does every semester -- 40"x60" to 40"x72", from 45 negatives. I turn around two of the Omega D5-XL's to project the images onto the floor, the paper is laid directly onto t he floor. The prints are see-sawed in troughs...one student on each end of the print. For the class critique, the prints are tacked to the outside of the art building...impressive to see 24 big prints on the wall!