Even among Audi’s famously beguiling automobiles, the A5 is a serious looker. As a coupe or convertible, the A5 and the sportier S5 have the sort of fine proportions and sumptuous accommodations that call to mind their corporate cousins, the Bentley Continental GT coupe and GTC convertible. And with the debut of the fearsome 2013 RS5—the coupe, which went on sale here in July, and the forthcoming cabriolet, which debuted at this year’s Paris Motor Show—Audi’s artful two-door gets a Continental GT-size helping of performance (or at least nine-tenths of one).