There are so many more choices in O Scale now than at any time in the past. I guess lusting after really good passenger cars is ok as a hobby, but in reality the current selection is mind-boggling.
Granted, we are on the O-27 forum, and most of you need the shorter versions (difficult to see how correct windows will fit) but if it is scale length you want, it is darn near all out there. My scale 2-rail collection is overwhelmed with really nice K-Line 21" cars. In my string of Budd cars I have K-Line, Sunset, Mac Shops, and even an ancient Kasiner - all are quite acceptable for 2- rail scale. Hard to believe that O-27 would demand better.
As for heavyweights - I have the PSC variety, but if I did plastic I would replace them all with the 3rd Rail cars. Except for the Harrimans . . .