The main Mario games have always sold huge so it's very likely that Galaxy will sell at the very least 11-12 million over it's lifetime but more likely it'll be millions higher, possibly 17-18 million (I would have went higher because of the Wii's potential installed base but games don't seem to sell as well as they did during the nes/snes days, even the best selling PS2 games never reached above 15 million with an installed base of around 118-120 million).