Originally Posted by Asterion
If properly trained, most. It's just that all of the elite heavyweights now train for 12-round fights (and then you have a percentage of lazy ****s who get tired).
NTM, with modern technique and strength training, an average guy from today, such as a Taras Bydenko or Jason Gavern type, would be like 135-10 in the 20s-60s and have a 90%KO rate inside the first 5 rds.
Those guys in the old days ate shots and slept for rounds. Even a fat POS like Sasha Petkovic would dominate the 40s or 50s.