ic-r, I'm a firm believer in using enlarging lenses at least twenty percent longer than the film's diagonal and I think fifty percent is probably optimal provided the lenses are used within their optimum magnification range. At least this was my personal experience thirty-five years ago with EL Nikkors and Rodagons of the time. I just don't have enough room in my little building to facilitate the print size I want and use lenses longer than "normal".