Psycho? Is that you?
As wonderful as the thought of a 2xHD6970 2GB may be, a single card will be one potent sum beach for the foreseeable future. Keeping the 'PowerTune' setting at a reasonable level and it's sure to be worth a good bit of money in a year or so.
You could sell the card (will certainly continue to be great CF value) and get some good cash - put it toward a new 28nm card.
If you only need to push a single HD6970-like card a 650w PSU should be fine (and nicely handle a new 28nm card in 2012).
It's worth a thought to save some cash for future goodness to keep that train a rollin'. An 870 motherboard and you have saved some more.
When you upgrade that video card, might be a good time to move everything over to a AM3+ motherboard.
Psycho? Is that you?