Let me try a different answer based on three years of riding and being allowed to fire New York Central J-1 Hudson's on NYC's Indiana Div. NYC was ending steam moving west and by about 1951, steam was only used west of Buffalo. Anything that had some miles left wound up on the Indiana, Ohio and Illinois divisions.
J-1's came in five sub-classes, J-1a thru J-1e. J-1e's 5395 to 5404 were generally the best performers since they had Worthington SA feedwater heaters. J-1d 5382 was usually assigned to the "James Whitcomb Riley" since it was the best of the engines usually assigned on the Indianapolis to Kankakee, IL leg. Some of the "foreign' power that came to the Indiana Div to run out their miles was in pretty poor shape. But one evening, I was riding with my favorite crew on train 405 out of Indianapolis. 405 of rumbled into the depot with "foreigner" 5279 on the front end. The east end firemen said it was a "pretty good pig" and told me how much pressure to use on the stoker jets. Just north of Indianapolis, the Big Four climbed an 0.4% grade for 12 miles and trains were limited to 40mph at the bottom of the grade. The 5270 ate up that grade and we were doing 75 before the top of the grade, something very few J-1's could do with 405's 8 car train.
In conclusion, engine performance depended on mechanical condition, fuel, skill of the engineer and fireman and outside conditions (ex; you have a 10 car train, it's 20 degrees outside and the communications whistle keeps peeping for more steam heat.)
Sad that no NYC Hudsons were saved.

Hal