Well, John gave me a kick in the pants so I just did 27 fully Die Cast bodied cars... 1 box, 3 hoppers, 8 ore and 15 tank (plus a fairly heavy but not die cast caboose) ...yanked them up the grade forward and then pushed them up the grade backwards with the Lionmaster Big Boy. They all followed through the divergent tortoises in reverse and straight through with switch in divergent position (non-derail spring loaded) without issue. So, without going to crazy I've got a pretty good idea about how much weight to add to the light rolling stock. I know there is a formula... but, I'm not a scale guy. I think I've another dozen or so die cast cars but this is close enough.