I guarantee you will be able to max out battlefield 3, ESPECIALLY if you crossfire it later on. Overclocking your card to 1050mhz would make it almost as powerful as a 6950.
Yes, I've seen cards overclocked so that they are up to 300 mhz higher, and since you are going to have the coolermaster HAF 912, and a dual fan design, I'm positive you could do that.