A 6990x2 is two SEPERATE video cards... it denotes someone using two 6990 video cards in Crossfire mode. Just like a 6990x3 denotes someone using 3 6990 cards in Crossfire mode.
So @ $722 per card your total would in fact be $1444, not misleading in any way. Keep in mind that the MH/s are averages based on user input, so YMMV.
Thanks for the clarification!
It really depends on your usage model. The 5770 is currently the best (readily) available performer when comparing power consumption and initial costs. If you're looking for the most performance you can cram in the least available space and the up front money isn't a huge concern, go for something like the 6970.
Using the bitcoin profitability calculator
and just changing the hashrate, cost, and power use of the video cards (not including the rest of the PC costs/consumption), the 5770 @ stock shows a $1.67USD/day profit with a 66 day "break even" (the card paying for itself). The 6970 shows a $3.44/Day profit with a 99 day "break even." Of course these calculations don't account for the difficulty going up, but it shows that long term, the 6970 is the more profitable card.
Of course, a lot of us little guys can't be dumping $340 here and there, which is where a card like the 5770 shines. We can only hope that video card manufacturers don't notice these values and adjust their profit margins accordingly.