Here is something
for you. I would go for one HD6950 and I usually buy Asus, though I haven't read much about HD6950/70 because it's not available in my country yet, but you could compare Asus's card and Sapphire's for instance. Asus usually offer one year more warranty than Sapphire, if warranty is important to you.
If you are lucky to get an older version of HD6950, you might be able to unlock it to HD6970 without any problems (more info here