The Q's Hudsons are some of the most underrated steam locomotives. Something truly eye-opening are the 'before and after' augment numbers for the S4b reported in the Timken ad in the '47 Cyc.
It should also be remembered that one of the engines achieved 112.5mph on test, which is pretty good anywhere. To put that in perspective, that's about 10mph faster than the ATSF's 3460s, with taller drivers and more advanced construction, could manage, and right up there with the best ATSF 4-8-4s.