The Beseler 23C will do up to 6x9cm negatives. If you wanted to go into an orgy of customization, you probably could build a lamphouse for it that would illuminate 4x5, but it would not be cost-effective. But the 23C is a terrific enlarger (I have a spare one sitting around as well) and I would be using it were it not for the fact that I do mostly large format work now and I have a Beseler 45M-series (I forget which one it is, MCRX? MC? blue chassis). The 23C is very rigid and solid. You can flip the head 90 degrees to project on a wall if you want to print really big. The 23C and the Omega D-series enlargers were the mainstays of school darkrooms for decades, for a very good reason - they're well nigh indestructible. Do check the elevation mechanism on any one you look at to make sure it is smooth and doesn't slip when stopped. Also check that the negative stage and baseboard can be made parallel - bring a little level with you and first check the level of the surface on which the enarger rests. Then compare that to the baseboard, and the negative stage. If the baseboard is warped, it isn't the end of the world - that can be remedied by a trip to Home Depot to get some good 1/4" plywood. If the negative stage is bent, walk away from it. It is possible that it can be fixed, but it is not cost-effective.