It's already outselling GT4 in aligned launches:
5 weeks worldwide:
GT5 is completely destroying GT4 in the past few weeks, despite the weaker first week. I think this happened because a lot of people were confused about the release date, and advertising wasn't able to kick in as early as it was supposed to. In EMEAA, GT5's 5 weeks has already outsold GT4's 10 weeks.
I predict that GT5 will go on to outsell GT4 by at least a million. The strong momentum of the game should continue into early 2011, and this is all happening despite a very weak Japanese market. Europe is loving this so much. I think the reason for all this happening is that GT4 was produced at the height of PS2 piracy, and that PS3 piracy is still virtually non-existent.
Anyway, to all the people who thought GT5 would sell "below Forza 3 or GT5 Prologue", "just 5 or 6 million", those people who said "PS3 userbase is too small", "It has bad reviews", "Forza is the new king of racing", "GT is on a decline", blah blah blah blah blah...
(Btw, Forza 3 sales, heavily bundled, over one year later: 4,405,464)