My modern coal dump car had a habit of dumping unexpectedly when going slow over a switch that was on a hill. My grandpa's old log dump car? Never ever dumped unless I was over the accessory track. I like the post war cars in general and I'm currently pulling them around my test loop with postwar and modern locos. I think the weight is more fun to pull than a lightweight car. It seems like they track better. My 3472/3462 (I think) milk train is one of my favorites to pull.
I would venture to guess you'll be needing to repair less shoes going slower though.
