I would go for a Crossfire instead a a card with two GPU's onboard. The reason is as I understand it you can't disable one of the GPU's on a dual GPU board if you have a game that does not work correctly in Crossfire mode. Plus with by going with two cards they are usually clocked higher than two GPU boards.
With a double GPU board what you get is the two high end GPPU's downclocked because of heat limitations. Drop down to the next lower single GPU board and get two of em and you invariably get more performance for a lot les money.