MGS3 did 4M on the PS2, and it's pretty safe to say MGS4 won't do as much. MGS fans are numerous and loyal, but there will be far less of the people who'll buy it just because it's a great game on a system they own, and a lot of the people who like the series are perfectly happy waiting for the remake to hit the 360 and/or PC in a year or so. I expect the PS3 version of MGS4 to end up around 3M lifetime.
Gears 1 did 5M, but it had the advantage of being the first excellent shooter on the 360, as well as bringing something new to the genre. The sequel has way more competition, and it remains to be seen how innovative it'll be. I'm guessing sales will be at least somewhat lower than with the original, but still higher than MGS4.







