There are good reasons to go either way here. But Iran at his best is at a sleight advantage,,but one Mugabi bomb could change that.
I really don't think Iran could withstand Johns power for too long. But if he did the longer the fight went the more it would be in Iran's favour. Curtis Parker was a hell of a middleweight at one time- supposedly beat up a young Hearns and ran him out of the gym in Philly- and Curtis had a very solid chin. John crushed Curtis in ONE round and was the only boxer to ever do that to a young Curtis.
I'll go with Barkley he always fought at Middleweight until he moved up, Mugabi was mostly a Jr Middleweight was he not ? until he moved up to fight Hagler. I think the extra size and strength for Barkley would be the difference.
Mugabi went toe to toe with Hagler and made him **** blood. There's nothing amusing about prime Mugabi and while I wouldn't write Barkley off I feel he's working uphill here against a huge hitter with a 'can't be beaten' attitude. Post Hagler Mugabi I feel was a broken man and Barkley would handle him.