8GB of RAM doesn't hurt.
12 is simply overkill for the vast majority of users.
Also, HD6970 ftw. Just one. It will keep up with any game you throw at it, and then some. Depending on the resolution you tend to game at, and settings you might enable (plus texture overhauls, or whatever, in some cases), the 2GB of VRAM really is quite nice to have, too.
Oblivion has a history of preferring ATI (now AMD) - and I can only assume that's still the case, to some extent. Per dollar, I mean, natch.