IMO, Benvenuti's style was wrong for Benn. However, I think Benvenuti ranks higher achievement-wise. As for the actual fight, this could go something like this: Nino was a good aggressive boxer. He keeps off a super-aggressive Benn for a few rounds and gets ahead on the scorecards. But suddenly, Benn finds the range and Benvenuti is in deep trouble. He tries to fight back, but Nigel is just too rough. The referee stops the fight somewhere in the middle rounds.
I think Benvenuti would try and avoid Benn's early bombs and keep boxing, with Benn's aggressiveness & power he would have his moments. But as the rounds progressed Benvenuti would slowly take over. In a twelve round fight Benn might have enough pionts to take it. But over the Fifteen round limit, Benvenuti would close strong and sweep the championship rounds for the decision.
Well actually there is still: Chris Eubank, Alan Minter, Vito Antuofermo, Rocky Mattiolli,Mikkel Kessler, Randy Turpin, Oh & by the way: Joe Calzaghe! Just to name a few.