I'd wager that the last major open shotgunning competition (not restricted to S x Ss) won with a S x S was won by Billy Perdue, of pigeon shooting fame. mel5141 could probably tell us the exact last championship Billy won, as the two were close friends for many years. Billy passed in 1997, but was a powerhouse on the clay ranges and live bird shoots around the world. He held many national records.
In an interview, Billy said that pigeon shooting was a game of elevation, which is why he favored the S x S for it. As I understood it, he believed the two barrels gave his peripheral vision a clearer idea of where he was, elevation-wise, as he focused hard on the pigeon.
SRH
