AMD is supposed to have new cards this week. I would at least wait for that.
If you upgrade, you want it ti be a major upgrade, or you can be disappointed if you do not see a big jump in performance.
Today, amd has no single gpu card that is a really big jump over the 7950. In that case, a 7950 cf would at least give you higher average fps.
The problem is that dual card drivers are still having problems with lagging. It is getting addressed, so you could bet on ta future fix.
If you go to a GTX780 superclock, that would be a significant jump and all you need for a single monitor.