Anyway, on topic I think DQIX could manage it, but it's not a sure thing. I do expect DQIX to continue outselling DQVIII in every market though, and DQVIII shipped a whopping 6.8m worldwide. DQIX will ship over 7m when all's said and done, guaranteed.
FFXIII basically had no legs in America (selling under 50k it's 2nd NPD), but it may resurge when it hits bargain bins (something less likely to happen for DQIX imo, given it's a Nintendo published game in the west). An International/360 release in Japan may yet also push it over 2m there imo. Still, with clever rereleases and budget pricing in all regions, I could see FFXIII also passing 7m eventually.







