There was a difference between a standad Cup car and an updated GT3 997 in 2007. You could buy a kit at Weissach which contained in its expensive form a higher rear wing, wider wheels and a bit more engine horse power. For 2008 you can buy a real GT3 car at Porsche. Here is a link to a (german) story about the model:
http://www.projectlemans.de/content/view/3831/172/