Aston Martin's new Zagato race car looks fantastic. But the real highlight here comes courtesy of the car's completely unsilenced 6.0-litre V12 engine. It produces a mammoth 550bhp, which is transferred to the tarmac via an automated manual gearbox borrowed from the Aston One-77. So what is this stripped out racer like to drive? Here, Jamie Corstorphine finds out at Gaydon's high-speed test facility.