There is no doubt that GT5 will be the best selling PS3 exclusive but I hardly think it'll move more copies in NA than in Europe/Others.
And I'm not too confident it'll sell over 10 million either. I think it can manage to pass 8 million lifetime though, it depends on how big the installed base becomes throughout the gen and this title will keep selling till the end, GT games have legs that I've never seen on other games (GT 3 stayed in the top 20 for 4,5 years here and top 10 for nearly 3 years).