I also share Richard's sentiments regarding diesel helpers, but have to acknowledge that in times, they are justified. Back in the halcyon days of GCR steam, it was not uncommon to operate trains of 13 cars to the Canyon. GCR has one 6 mile stretch of 3%, so they'd put the days steamer on the point and add whatever helpers were necessary. It worked and would have been prototypical during the time of steam/diesel overlap.
Now there is one steam locomotive in America today (actually 2 exist) that could manage this length of train unaided, and that's the C&O 2-6-6-6. Don't think that idea hasn't been kicked around and dreamed of in the past! I don't believe some of the negative comments that have been written about the Allegheny being neither fish nor fowl, they were perhaps the ultimate mountain machine. And with all that weight on the drivers, they still had room to grow as it were, in having the boiler pressure increased from the as-built 260 lbs.