Low profile has nothing to do with the width, it's the height he's talking about.
I'm thinking 4670, let me see..
This 4650 supports Xfire, they claimhttp://www.newegg.com/Product/Product.aspx?Item=N82E16814131180&cm_re=4650-_-14-131-180-_-Product
I would be more willing to bet on this Sapphire thoughhttp://www.newegg.com/Product/Product.aspx?Item=N82E16814102829&cm_re=4650-_-14-102-829-_-Product
Still, 4650 is not a great card. CF would be better than a single 9800GT though, I think. Perhaps only a bit though.
You would be better off getting a taller case.