AMD has published the Catalyst 12.11 beta 7 driver, you can download it over here. This release includes performance gains for CrossFire configurations in Call of Duty Black Ops 2. The changelog of beta 6 and 7 is listed below:
AMD Catalyst 12.11 Beta6 resolves the issue with engine and memory clocks running too high when the GPU is idle. Clocks will now run at the proper level when the GPU is idle. This issue was only observed with specific displays and was observed in the AMD Catalyst 12.11Beta 4 and AMD Catalyst 12.10 drivers; The AMD Catalyst 12.11 Beta6 has replaced the AMD Catalyst 12.11Beta 4 driver that was posted Oct 23, 2012.
Additional update found in AMD Catalyst 12.11 Beta7
Call of Duty Black Ops 2: AMD CrossFire performance has been improved in the AMD Catalyst 12.11 Beta7 release (especially at higher resolutions – such as 2560x1600)
Please note that AMD Catalyst 12.11 Beta 7 includes all of the fixes found in previous versions of AMD Catalyst 12.11 Beta