This game won't double it's sales for first week. So it won't sell 600k and won't outsell Mario Kart. For comparision those are first week/first day ratios for biggest PS3 games in Japan:
PS3 Devil May Cry 4 (209/140) : 1,49
PS3 Gundam Musou (175/117): 1,5
PS3 Yakuza 3 (178/113): 1,58
PS3 Winning Eleven 2008 (147/107): 1,37
PS3 Hot Shots Golf 5 (168/103): 1,63
PS3 Gran Turismo 5 Prologue (109/50): 2,18
PS3 Bladestorm: The Hundred... (62/40): 1,55
PS3 Disgaea 3 (58/40): 1,45
Most games sales around 50% more in first week than in first day, so 450,000 for MGS4 is a reasonable number (maybe 500,000 with bundes).