I don't think it's faster per se, but rather more drivable. I think there comes a point when F1 cars are limited by how much water there is on the track before they start aquaplaning and stalling the diffuser, and so the bastardised DTM car they use as a safety car can afford to push more.
On top of that - the car sounds gorgeous. I watched it doing laps around the Singapore circuit at night (before the race weekend) and the way it sounded, especially with echoes bouncing off the circuit walls and the surrounding buildings, sounded absolutely magnificent.