Don't get me wrong here. I'm no expert. But I've been asking the same sort of questions on the barn about my ride ('47 Merc). From what I can make of it, the difference is in the softness of the lining material. Softer lining = stronger braking but more wear. Hard lining = not-so-strong braking but better wear. If you don't plan to do a lotta miles then I'd go for a softer lining material. There's a guy here in NZ has his own shop. He's called FlatheadTed. He seems to know a hell of a lot when it comes to old school brakes. He's on the barn too. Hope this has helped!