When they did the Coyote engine in 2011, the base GT brakes became the 13.2", 18" was the smallest wheel on those cars. The V6 PP cars, and all 2013-2014 V6, got the 05-10 GT 12.4" rotors.
On the S550, V6 and base Ecoboost have 12.5" brakes that 17" fit over. Ecoboost PP and base GT have...