It will very much depend on the marketing...
If MGS4 level marketing then WW~200k
If GT5p/GTA4 marketing then WW~350k
But it should have excellent legs mainly due to the fact that it will be one of the only games that will actually improve in quality over time.... (and for free)
PSN ID: T_Gears
End of 2009 ltd sales:
Wii = 67-68m
X360 = 38-39m
PS3 = 34-35m
Prediction: The PS3 will surpass the 360 on weekly sales after it drops to $299 on all regular weeks (no big releases).