When I first ran the game and it set all the settings, it selected the highest settings possible. It's running them just fine -- I haven't had to reduce them at all.
So, for all you Mac users who like to play the occasional PC game (I also play Civilization V just fine), go ahead and go for it. But use Windows XP -- Vista and Windows 7 are not ready for prime time yet. I was pleasantly surprised to find that Microsoft support let me install WIndows XP and activate it even though it had already been activated on another machine. They said I could activate as many computers as I wanted with XP! Very nice of them.
p.s. Am enjoying the game -- lots of fun.