This article on Rocky Marciano’s Punching Power shares a number of famous boxers’ comments on Rocky’s devastating strength, but I enjoyed this (apocryphal) bit of science from the U.S. Testing Co.:
“Marciano’s knockout blow packs more explosive energy than an armour-piercing bullet and represents as much energy as would be required to spot lift 1000 pounds one foot off the ground.”
— Boxing Illustrated, December, 1963