We have two 5 ton Plymouths at the Pacific Coast RR and we have double headed them to move around some of the rolling stock. They came from the Apache Powder operation in Arizona I believe. However a few weeks ago I found myself in the middle of two trains with a 22 ton steam loco in the rear and a IRCA caboose and 25 ton steam loco in front. Well I got the whole lot moving, but it wasn't without difficulty. What we wouldn't give to have a 20-25 tonner around here.
Your right that about all these lokies are good for is a glorified backyard operation. Hey if you need some rolling stock to match, our GM is selling off his. (Flats & Boxcars from APCo)