The Koenigsegg Agera RS is officially the fastest production car in the world having taken the record from Bugatti, who until now held the highest speed for the fastest convertible with the Veyron Grand Sport VItesse. Visiting Whitesse's garage, which just so happens to contain both of these cars - let's put them up against each other in a head to head... to remove the roofs and transform them into convertibles!br br The Bugatti Veyron Vitesse reached 409kmh or 254mph, and that stood as a roof-open production car speed record until November 2017 when Koenigsegg took a run with the Agera RS.