I just noticed SMG passed Halo 3 in Others about 2 weeks ago, so I thought I'd give this 7 month old thread a bump.
I think thesource's predictions are looking mostly pretty strong, but 18mil and 12mil lifetime seems a tad ambitious for both games to me now. Galaxy will definitely pass Halo 3 world wide though. Depending on a 360 pricedrop and other holiday factors, my (very) rough estimation has SMG pasing Halo 3 sometime in the summer or fall of next year.
I see Halo 3's lifetime total being closer to 10.5 or 11 million, mostly because Call of Duty IV (and possibly Call of Duty V) stole a lot of Halo's thunder/selling power--probably more than most of us initially expected.
I've got more wildy speculative theories about Galaxy's final total. Basically, I think it will go on to sell a good 14 or 15 mil, but it will lose a some of its selling power when Miyamoto announces Galaxy 2 at next years E3.
http://vgchartz.com/swlaunch.php?reg1=All&game1=Super+Mario+Galaxy+-+Wii®2=All&game2=Halo+3+-+X360®3=All&game3=Call+of+Duty+4%3A+Modern+Warfare+-+X360&weeks=100
