I have moved over to the more scale size view of things the past year plus, so I prefer the 21-inch cars. The overhang doesn't bother me as much as when I place my 85-foot cars (Atlas 21-inch NJ Transit Comet car; MTH 19-inch Tri-Rail car) next to each other which makes the MTH look even more stubbier than it already does. If I could purchase some K-Line 21 inch Bombardiers and have the Tri-Rail palm trees and sky livery accurately placed on it, I would do it in a heartbeat. I'm on the wait list for the 21-inch GGD Amtrak Viewliners so that will make matters more interesting. And that's just the passenger stuff. I haven't got any freight rolling stock yet and I'm all about 89-foot Autoracks.
That being said, I only have room for O-72 curves at the maximum. Anything larger and then I would be running in a literal big circle instead of a quadrilateral with rounded edges.
This is what has led me to purchase more and more HO stuff recently so that I can get my desired exact scale look within my allotted space - off topic but related, my train room plans have now switched to primarily HO with O mixed in on one side - but I will still look at getting only scale sized O stock to run on my ceiling layout (where the O-72 overhang is hidden) and at the club. Like Jonathan, I like passenger trains first, but my desired future commuter inventory (NJ Transit, Metra, SEPTA, LIRR, Metro North, Rail Runner, etc.) will have to be done in 1:87 with a few exceptions.
