I think Halo is the game this year that will push the most XBO's...
Forza H will sell well, and will push consoles, but not anything massive.
Sunset Overdrive, I just don't see doing that well.. but then i am not a fan of it's art style.. the E3 trailer also put me off more
Halo will be massive, but i think many users will already own an Xbo for it, I mean these are the hardcore who probably are waiting for a Halo.. early adopters who buy because they know what they are going to get. So I expect the game to sell massively well, and for it to push consoles but probably not a massive amount.... and its coming out toward Xmas... so a pretty good combination.