I have done 20x16 Ilford Multigrade Warmtone in a Jobo print drum without any marks. The bigger risk, in my opinion, is creasing the paper getting it out when wet. I did a pre-soak, develop, stop, fix, rinse cycle on a manual roller base. My CPE-2+ cannot handle anything above 11x14. The only reason I do this is because my space is tight for tray processing at this size, and the drum is easier for a couple of sheets. I wash my 20x16 in a Versalab 11x14 washer with a substitute insert.