Ever since the Bugatti Chiron was launched, with a 261-mph speed limiter, we've been desperate to know what it could manage if let off the leash. Now Bugatti has done that at the vast Ehra-Lessien test track in Germany; the car smashed both the production-car record and the 300-mph barrier. Factory test driver Andy Wallace, who previously set production-car records in both the Jaguar XJ220 and...