Thanks for all the information. I am covered at 600mm with the Fuji, but the 800mm Ronar looks interesting. I also have a line on a 35 inch Aratar which has been mounted in a shutter.
Actually, Kowa graphics lenses are extremely hard to come by here, I have seen exactly two for sale here in the last 4 years. Does anyone know exactly which one of 240mm would cover 12x20? The SSXL is would be a first choice, but the $1000 center filter has me scared off a bit.