Bob Foster had frightening power. [ame]http://www.youtube.com/watch?v=Rm0wuLHykU0&feature=related[/ame]
There were some Mexican bantamweights in the 70s who could really bang in the form of Ruben Olivares, Carlos Zarate and Lupe Pintor.
How did his power do at HW? Guys like Langford, Ketchel, Fitz proved theirs from MW-HW. Freddie Steele deserves mention he was the only person to ever stop guys like Overlin and Dundee or drop Jones and all of them had over 120 fights, in what was one of the strongest MW eras ever.
Going by the record, probably Fitz. Of fighters where there is a great deal of footage available, I'd lean towards Jackson.
Why don't people mention Naseem Hamed, he showed that even his weight class can have "heavyweight like" KOs.