Based on this, from Psychotext at GAF, he put together the attach rates of some big PS3 and 360 sellers. The amount of the install base (at the start of the month the game was released) that bought it, heres the top titles without Halo 3:

360:

Gears of war 34.6%

GTA4 27.1%

Modern Warfare 2 25.5%

Call of Duty 4 22.1%

Madden NFL 08 15.2%

Assasins Creed 13.8%

PS3:

GTA4 34.3%

MW2 20.7%

MGS4 17.5%

Madden 09 12.7%

COD WaW 10.6%

Killzone 2 8.5%

Now what, you ask, was Halo 3's attach rate? An astounding 53.3%. Blowing away any other title on the list.

Granted, these attach rates will fall, and drastically, as the userbase expands. However, if even a conservative 33% of Xbox 360 owners buy Halo Reach in Fall 2010...7 million sold first month is easily within reach.

Also, wasn't MW2's 4.2m first month 360 an NPD record? I cant imagine any PS2 game beating it, and I dont think anything earlier had such huge debuts, it simply didn't happen back in say the SNES days. So it looks like 360 holds the record, and Halo Reach will shatter the record again on 360.

MSFT better push a huge marketing campaign if they want the Reach numbers to beat Modern Warfare 2.

No... that'll mean it'll sell over 10 million first month... just no.

Depends WHEN in the Month is launches.

If it launches the first week, it's possible...

No way.

2 million sure

Knowing the nature of the beast, the game will sell something like 70% of its total sales withing the first week or something, so the same launch date as Halo 3/ Halo ODST should be good enough.

just above 2ml first month for halo reach but god of war 3 will be huge

Halo Wars and ODST have damaged the franchise, while quality games, theyve relegated Halo to something thats nowhere near as much of a fuss when released.

7 million? lol