If we're talking about the Duran that beat Moore, then Nando would recieve a brutal ass whupping. Duran TKO 10.
At super welterweight ? Not Duran best class, that's where he got literally KTFO by Hearns... But Vargas ain't no Hearns. Duran would probably KO him in the mid round. He was THAT good, even 3 classes above his best weight.
I think this is reasonable, and only the duran that fought moore as well, roberto was pretty much shot at 154, i can't see him stopping a prime vargas, it took tito 12 who punched far harder than duran at 54, duran by UD
in his prime pre-tito duran wouldnt have knocked him out but just out hustle and outwork him to a ud, vargas was strong, real strong and people forget just how much heart and chin this guy had, it took vicious punching trinidad multiple flush shots late in the fight to end it(and low blows) vargas wouldnt have been stopped by many in and around welter-jr middle in his prime
Vargas would be competitive for a few rounds then Duran would take over and probably win on points or late stoppage. Duran has too many tools for Vargas.