Thanks archean. I googled around for a while and couldn't find anything as comprehensive as the article you linked, it was really helpful. From what the article states, two 6770's crossfired is equivalent to a 6970, which answers my question :-)
It looks like that crossfire option is superior to the single card option.
Have you ever actually run crossfire, the drivers are terrible and the issues that the OP will deal with do not justify the performance, not to mention that minimum fps will be piss poor, the OP is better off going with a single 6950 or gtx 560ti imo