I'll just throw this in to add to the confusion.
I have the Lionel CC ESE from 2005. All of my loops are 0-72, so that it what I run it on. The owner's manual for the engine states that the min. curve for the engine is 0-54.
I also have the optional PT tender made for the engine, that I have not run yet and is still in the box. The owner's manual for it states that it requires a min. curve of 0-54 and that there is a extra drawbar included for closer coupling for 0-72 track.
Since I have no 0-54 curves, I cannot verify this. I do know that the PT tender on my MTH Dreyfuss Hudson requires 0-72 curves.
See page 2 of the owner's manual.
PT tender manual