Probably 10m - 11m.

I will say that I haven't been interested in Halo since the original Xbox, but Halo 4 and its Metroid Prime pedigree certainly has me intrigued.

I'm not sure, but I think that I remember hearing that ratio between Halo 3 to xbox 360s was 1:3. 

I bet it won't do 10 million.

Any takers?

Fair enough then. I think it'll be safe to say that it can get to 10 million LTD. Beyond that, no idea, so I'm going with 10 to 11 on the poll. Even ODST managed to get 6+ million and that was considered pretty weak (depending on who you speak to), so 10 seems entirely viable.

I believe that Halo 4 will outsell Halo 3. It will get to at least 12million.
1) More people will buy it as compared to Halo Reach, only because there is a "4" after Halo.
2) There are more Xboxes in homes as compared to the date of Halo 3 being released.
3) People can't wait to see how 343 does compared to Bungie.
4) Microsoft is pulling the same moves with Halo 4 as they did with Halo 3. Mountain Dew Game Fuel, tons of commercials, and extreme Hyping up. Microsoft is best at advertising.
5) Analysts predict that CoD has hits peak and should only decline in sales. So what will all those CoD gamers get when no BF is being released? Halo.

There are tons of reasons why Halo 4 has the potential to outsell Halo 3.

Honestly, I don't think so. It's being released too late within the 360's life cycle. It might surpass Reach's sales, but I highly doubt it'll reach 3's. I'm putting my money on 10.5 million lifetime.

The counter point to that is that a larger number of XBoxes do not necessarily mean larger userbase.  I've had to purchase a new 360 since Halo 3 because my old one broke.   So that's 2 XBoxes, but still just one of me.  Second, some XBox owners may have stopped using the console already with this gen winding to a close and it's just sitting in storage collecting dust.  

Bungie fanboys and loyalists may not support the game and want to see 343 fail.  

Good mix of agrees and disagrees i like.

It'll sell 10+ million for sure.

11-12.5 million is my estimate.