Well, it already topped out every PS3 game, so no real competition there. GT5 will sell very well, but I'd be shocked if it does much more than 8m units. The best selling exclusive so far hasn't even broken 4m units. It would also make GT5 the best selling PS3 game ever by 2.5m units (looking at current software sales)
As for X360, I can see it getting ahead of Call of Duty, so it should be able to hold its own there too.
The one unknown, is if either Sony or Microsoft have a breakaway success with a title, like GTAs of the past, or a new Halo 3.








