The weird thing about competing in the "fastest video card" space is that it's always these dual gpu cards which pay significant performance penalties to split the workloads between the two chips as compared to 2x a single gpu. The difference between a winner and loser in the dual gpu shootout (when things are pretty close otherwise) probably amounts to the quality of the gpu splitting code in the drivers (the same stuff as the sli/crossfire code as I understand it).

While there is no doubt that real world tests of these dual gpu powerhouses will show who can eek out the most fps, if you really just want to compare chip tech vs chip tech it's probably better to compare at the single top end gpu vs. single top end gpu level.