2014 Camaro Z28 ran 7.37 at Nürburgring (light rain at times)
The Camaro ZL1 ran 7:41 at Nürburgring.
I haven't been able to find any times for stock Boss 302 or GT500.
I did find a race prepped(upgraded tires, brakes, suspension) Boss 302 running low 8s at Nürburgring.
Ford has the run times but guessing they must not be that great since they haven't been published.
If the 2015 Mustang is built right I expect to see a Mustang besting the Camaro numbers above.