I dont get you folks. Do you want to game on a MacMini? get a freaking iMac, it ships with GT 640M and GTX 675MX
What kind of serious gamer wants to game on a Macmini??? Heck, even gaming on a Mac is not that advised, if you wanna play current titles with MAX settings.
Having said that, I was able to play Bioshock (2006) Max out on a 2010 MacMini (m320), wich is inferior to HD 4000