I had such issues in the past and it was a combination of factors.
You will have to swap CPU ,memory ,the video card and the hard drive unfortunately , to see if the issues goes away.
You should also take a look in the Event manager to see if there is any error (with it s code) occuring at the freeze time.
First thing you should do is some memory testing ( or swap).
Use Memtest and run 25 passes of it on both sticks ,then on each one of them and then in all slots with any of them and see if any error occurs.
It can be very well an unmatched pair of RAM sticks that in specific stress conditions generates some error in some driver.
I am owning a 6950 unlocked to 6970 ,running Catalyst 12.1 ,under W7 X64 up to date and neither BF BC2 neither BF 3 are behaving.So you could try running this driver to be on the safe side video driver wise.
A security suite can give freezes as well ,if you are using such remove it temporarelly.