They look pretty evenly matched to me other than the Shelby having the driver mod. Couldn't tell what year Z06 that was, but if it was an 06/07 it should have walked the Shelby with a good driver. A Z06 is about 800 pounds lighter, has the same horsepower, and is about evenly weighted at 51/49 verses the GT500 being more around 54/46.
http://www.trackdawgz.com/Videos/MFBA%20Z06%20Chase.wmv