as hard as it is to find 6950 CF reviews that match games/benches with the 7970, the 6950 CF beats it in most all things I found
I already have 1 6950 for 1080p...so I'm going to risk hassles and crossfire
Keep an eye on Toms Hardware charts if you're looking for a direct comparison:
http://www.tomshardware.com/charts/2011-gaming-graphics-charts/Gamer-Index,2673.html
Although for the moment it doesn't seem to have the 7970 listed, but hopefully it comes up soon (pretty sure they do list engineering samples)
Also keep in mind with those charts that you cant simply minus the results and say this card is xx% faster than that card, its relative to an index so you have to perform a simple a divide function.
6950 2GB CF here I come. Hope it works right, I got my gigabyte z68xp-ud4 from there too
Just to let you guys know, CFx (and SLI -im not picking on ATI-) suffer from a phenomenon referred to as microstutter. You can read up on it here:
http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html
If you already have a 6950 then by all means crossfire will be worth it due to the price saving, but I would HIGHLY RECOMMEND not going down the crossfire route for those of you without a preexisting 69xx card (explained below if you can be bothered reading).
As the 7970 is ~40% more powerful than a 6970 and a 6970 is ~15% less powerful than a 6950 that leaves the 6950 as being ~60% slower than a 7970. Just speculation for the moment, but if you consider that the 7970 will most likely overclock better than the 6950, by say about ~10%, we could say that the 7970oc'd is ~80% faster than a 6950oc'd. Considering crossfire with a 6950 yields ~90% extra performance, thats only 10% extra performance but microstutter degenerates our perception of this performance, making the 7970 a better alternative (especially considering the power and heat savings not to mention the driver headaches with cfx).
*All results were taken from Toms Hardware Gamer Index for 1920x1200 and solved for by simultaneous equations, other resolutions may prove to be different.