Don't know what a Berkshire 2-8-4 can pull but an older the older Williams(pre-Bachmann) S-2 Pennsy steam engine I have can pull about 27 Lionel post war hopper or gondola cars behind it before it derails on my 042 curves. I didn't have that many modern freight cars to use with the S-2 steam engine.
Also I have three Williams SD-45's and they have differant wheel designs. The one with traction tires does best as for pulling but can't handle any Lionel add-on track(145C contact for highway crossing lights) accessories, as it has only two sets of metal wheels on each truck assembly and one set of plastic wheels, stops cold at the accessory contact. My SD-45 with all metal wheels(no traction tires doesn't pull as many freight cars but doesn't get stuck anywhere either.
Lee F.
Also I have three Williams SD-45's and they have differant wheel designs. The one with traction tires does best as for pulling but can't handle any Lionel add-on track(145C contact for highway crossing lights) accessories, as it has only two sets of metal wheels on each truck assembly and one set of plastic wheels, stops cold at the accessory contact. My SD-45 with all metal wheels(no traction tires doesn't pull as many freight cars but doesn't get stuck anywhere either.
Lee F.