I hate to disagree but the "Big Boys" weren't the biggest, most powerful or anything.Nice photos, Chris!I know how much you like steam engines. Here is the World's largest steam locomotive, Chris! It's at a railway mueseum in Green Bay, Wisconsin. I remember going to this mueseum when I was a kid.
http://nationalrrmuseum.org/visit-us/exhibits/union-pacific-4017-big-boy/
They also had President Franklin D. Roosevelt's personal train compartment! I remember how plush it was with it's elegant furniture seating.
Most continuous Tractive force - N&W Y6b's after 1952. (170,000lbs)
Most boiler HP was probably the C&O H-8 Allegheny's or PRR experimentals.(somewhere in the 7500 range)
Longest were the Erie triplex or Virginian Triplex. The Big Boys got the name because someone snapped a photo of one while it was being built and on the front cylinder somebody wrote in chalk Big Boy.











