There is actually an off chance for Benn here in my opinion, though as you've said, Hagler would be favourite. Hagler has the iron chin, he also has the fighters heart, but he is not anything like as awkward as, say, Eubank. The point where Benn is concerned is that he is very difficult to discourage - he punches with real power and comes ahead. So he'd be after Hagler every second of every round. BUT. Here is an example of a fight where Hagler could benefit from the southpaw stance. If he utilises it properly, i'd go for a mid-round KO.
If Marvin fought with the respectful stratagy he initially employed against Sibson, likewise he would probably defuse Benn and stop him mid-Fight,
I think that Marvin feel like he had something to prove against Benn, as I think Marvin fealt in most fights. He would need this emotion. I believe Benn would rock Hagler early, as did Hearns. This would make Hagler want to get Benn even more. Benn would over power Hagler in the early rounds, and would probably lead after five. Then, things would change. Benn's heavier shots will have lost a bit of impact, and Hagler's more accurate shots will begin to show. Benn may lose a decision in a 12 round fight, but I don't think he hears the final bell in a 15 round match.
Benn going the full 12 with Hagler when he couldn't even make to the final bell against Eubank and Watson? A peak Hagler would box circles around Nigel and would close out the show within 5 rounds. Mismatch this one.
Benn was the last one standing against McClellan. Gerald hit much harder than Hagler. That is an easy discussion. I said Benn may lose a decision in a 12 round fight. That leaves the opening for a stoppage. I also said I don't think he'd see the end in a 15 round affair.
Wasn't Benn best at Supermiddle..eight pounds north of Middleweight? I never saw Hagler that heavy. I take Benn by TKO on cuts over Hagler in 7 vicious rounds.
Benn had the heart of a lion, as he proved against McClennan, but this is Hagler we're talkin' here, and he would stop Benn in 8 or 9, tko.
And Gerald hit much harder than Eubank or Watson. It's irrelevant. The gap in skills between Hagler and Benn would result in a demolition a la Sibson, Scypion etc
IMO Benn would be much more dangerous than Sibson or Scypion, he's a vastly more dynamic proposition. McClellen would have left Sibon and Scypion prone - fast. I still take Hagler tho, this is the sort of fight he will fare very well in. He takes a top shot and Bennis the sort of opponent he will be able to get the better of via boxing. I can see Hagler jabbing and fighting from the outside, surviving a few exciting exchanges and wearing Nigel down probably. This is a top matchup for excitement tho, even with Hagler boxing it would be electric.