@lego_my_eggo: I am not sure about the pre-order cars. It looks like the original Playstation.blog post, showed that you could purchase 1 million credits and in the picture above you can see that all of the cars are pretty standard fare.
I enjoyed GT5, but there were so many disappointments after playing both Forza 2 and Forza 3 that when you compare the games you can really see that in menu usability and online options Forza really wins overall. I am not sure if I will wait for GT7 or go ahead and buy GT6. But, like you, I'm gonna wait and see. Hell! I didn't buy GT5 until Spec II came out in Japan.