I believe that only the Sport models had the 338mm rotors. The 319mm rotors should have a 13WG or 13WL marking on the calipers while the 338mm rotors have a 13WH marking on the calipers. Here's the rotor diameter as indicated by the markings on the calipers:
13WH- 13.3"/338mm rotor diameter
13WL- 12.6"/319mm rotor diameter
13WG- 12.6"/319mm rotor diameter
This thread may also help:
How To: Upgrading to Sport Brakes (319 to 338mm)