Heh, I don't have the end all of Navi's, but, I know the one I do have is 4 TB HD's Raid 0, quad core q6700 CPU, 8 gigs of ram, dual 8800GTS 512 cards.
So, I can handle a decent amount, but the last time I ran FF12, it was... 2003? The Navi was "laughable" to today's standards. So I don't remember it being real hard hitting on the graphics cards/CPU, but I could be wrong.