Is there a reason you are set on getting 2 cards from the start? I would recommend at least getting just a single HD6950 at first and seeing if that is enough for you. I suspect it will be, especially if you unlock it into an HD6970.
Having 2 really fast cards is big overkill for your gaming needs.Unless your playing games like crysis or crysis 2 and must have every setting maxed out,then theirs no reason you should need x2 6950's.
On a side note,if you are running dual monitors or an eyefinity setup, getting a 69xx series card will be very helpfuly and boost performance because of the 2G of RAM.
Could you list some games your intedning to play?