Found another source:
http://www.edmunds.com/ford/mustang/2011/testdrive.html
So Edmunds ran a 13.0 in the GT and a 13.1 in the SS (Note: Different time , different place)
Car and Driver ran a 13.0 in the SS and 13.2 in the GT (Note: Same time , same place)
So I would say right now hanging on to the 12.7 is being a little nieve