Largest/heaviest steam locomotives: DM&IR 2-8-8-4 (699,700 lbs), Big Boy (772,000 lbs), Northern Pacific 2-8-8-4 (717,000 lbs), Southern Pacific AC-9 2-8-8-4 (689,900 lbs), C&O 2-6-6-6 (724,500 lbs), Western Pacific 2-8-8-2 (663,100 lbs). These weights were published in "Steam's Finest Hour", a book written by "Trains Magazine's" David P. Morgan, and released in late 1959. According to Wikipedia, the C&O 2-6-6-6 was erroneously weighed at Lima, and was re-weighed by the railroad (apparently prompted by complaints from operating crews, whose pay rates were determined by the weight of locomotives) and found to be 771,300 lbs.
The weight of the Virginian's 2-6-6-6's is a bit unclear from the historical record. Believe they were as heavy as the C&O counterpart, but are listed on websites as weighing 753,000 lbs.
