Great question and fantastic post. It was really helpful to look at all of those numbers and factors to determine my choice.
My general feel right now is that Halo has a more predictable pattern of sales than SMG could have. I think that there is a very large chance that Halo 3 will fall somewhere between 6-10 million. I think somewhere along the lines of 8-9 million being most realistic. Factoring in previous sales of the two games, the price of the console and the install base I think that sounds pretty good.
SMG, on the other hand, is a wildcard in my opion. It could sell anywhere on the low end of 5mil [although unlikely] following the decline in sales of mario console titles, or it could be an enormous breakout title that could approach 20mil in sales lifetime like The Source seems to think. I am leaning towards the latter slightly more. I think a reasonable range would be 8-15 mil, much larger because there is so much more in question. Halo 3 isn't changing a lot so it's garunteed to basically be the same goodness, but SMG is yet unproven and has a lot changed in terms of environments and such. It will have a larger install base and could have 3 strong markets as opposed to Halo's one. My uncertainty of crazy 18 mil numbers lie in the fact that I am really not sure if Japan will buy a console Mario like they have with the DS which is much bigger and more accessable than Wii. I'm thinking somewhere in the realm of 12 mil as my final guess though.
I think if SMG really takes off well with the casual market and Ninty gets plenty of consoles out there, the really interesting question will be posed of whether SMG can beat Halo in America? If this happens in the next year or two I think the writing is on the wall that the Wii will be dominant like PS was of previous generations.
