Here are the lap time records for Leguna Seca:
13. Porsche 911 Turbo 1:37.80 133 '09 500 / 1570
14. Ford Shelby GT500 1:38.69 131 '12 558 / 1733 Randy Pobst
15. Ford Mustang Shelby GT500 1:38.69 131 13 659 / 1750 Randy Pobst
16. Ford Shelby GT500 1:38.70 131 '12 558 / 1733 Randy Pobst
17. Mercedes SLS AMG 1:38.82 131 '10 571 / 1620
18. Chevrolet Camaro ZL1 1:39.18 131 '12 588 / 1838 Randy Pobst
19. Ford Mustang Boss 302 LS 1:39.50 130 '12 443 / 1652
20. Porsche 911 GT3 1:39.52 130 '06 415 / 1395
21. Porsche 911 Turbo 1:39.89 130 '06 480 / 1585
22. Porsche 911 Turbo S
http://www.fastestlaps.com/tracks/laguna_seca.html
If you take a look at the time for the 2012 and 2013 Selby GT500, it's identical.....extra power didn't make a difference.