Audi’s breathtaking 560-horsepower RS7 delivers true Supercar performance coupled with daily-driving versatility, writes  Road Test Editor Howard Walker Remember the Seventies? Back then; if you were a testosterone-charged teen, chances are your bedroom would have had a poster of a Lamborghini Countach pinned to the wall. Race-me red paint, scissor-style doors raised skywards, more air-gulping intakes than an F-16 fighter.  No doubt it would have been positioned right next to a p...