Benn would absolutely dominate and stop Duran while taking very little punishment. Duran would be so preoccupied with trying to evade the explosive assault of Benn , he would find little opportunity to mount his own defense. Benn wins purely because he is just too big fast and powerful for Duran.
I should add when Duran fought a great fighter or top fighter. On the same night Hearns stopped Duran, Duran could have beaten other guys in his range. Even with Hearns he landed some decent punches, but not clean enough.