I am glad we are talking about this because I will consider this when buying curves. I have no track right now and I have not designed my layout yet, so the curves are still up in the air. I am thinking about a U-shaped layout where I can walk right into the middle and yet have the ability to make long track lines by having them travel along the entire U perimeter.
I want a long and flat dedicated track line for my 736 Berkshire and the Madisons. Then I want another track line that is longer and much more sophisticated for my other locomotives, which are all Legacy. With the Legacy locomotives I will have the advantage of being able to run more than one locomotive on the same track line as well as incorporate climbs and descents. Curve size is my #1 consideration. The Madison cars that I have looked OK on 036 track, but I think they would look better with a wider curve size.
I am not buying anymore postwar equipment. I love the 736 Berkshire and the Madisons because they function well, look great together, and serve as my link to the past and the history of model railroading, but I only want modern equipment (passenger cars and coal hoppers) now to run with my Legacy locomotives. Minimum curve will be 072 without question, but I will now consider going 084 or even higher.