I've used a SINGLE Big Boy to pull 1,000 (yes, one thousand) boxcars. Granted, they were built-in paintshed ones, but I put together 50 cars, then made a consist out of them, then just kept adding to the consist until I got one thousand cars. I used the Robe River Iron route, and even then, the computer got maybe 5 FPS trying to move all thousand cars at once. I did get up to 27 mph before it crashed, though. GO BIG BOY!