What is Quadfire? do you mean crossfire? AMD got cought with not suficient driver support for BF3 , because just prior to launch EA/Dice added to the game without giving the card vendors time to spruce up thier drivers for that game. Evedently Nvidia was somewhat unaffected by this because whatever they added only affected AMD drivers. Once AMD had a chance to work out the driver issue thier cards are playing BF3 much better.
Then its obvious its the CPU thats the bottleneck the cards wont bottleneck that bad at an eyefinity resolution because they get 190fps in 1920 x 1080 so 5760 x 1080 i would think gets about 50-60 fps.