what do u use ur 6950s for ? not that u dont use them......mind shipping them to me ?
That provided a good laugh for me just before bedtime, lol! I could also use one of them providing its an XFX 6950 2G with a dual BIOS, lol. It would fill the 3rd slot on my system and make me feel justified to have a corsair 1000 watt psu.
Getting back to the OP's Q, I read up on several benchmarks THG did a little while back and id say in 75~90% of the time you will get a 20~90% performance boost in most cases with most games in several resolution settings. But as others stated, it will partially depend on if the rest of your system is up to par to not bottleneck those cards. There was also a 5~10% of the time you will get less frame rates than with a single card. I never got a solid understanding on the reason why but that was the experience they had with it. But overall it is a great setup and it prompted me to pick up a 2nd to CF myself and it is very nice.
What is the system specs that you want to put these cards in?