Thanks for the reply. I know that page, I look at it constantly when deciding what to buy.
I know that one 6990 would be best, but I can't find any store in my country that sells it, they are all out of stock. And I wouldn't like to buy it from amazon and wait for it 1 or 2 months. In a few days I would like to start mining.
And why shouldn't I CF them?
Personally I'd just go with the 2 x 6970's rather than wait.
And with regards CF, most people report lower hash rates and I experienced the same when I CF'd my 2 x 6950's