AMD released a hotfix which concerns the Fallout NV crossfire issue, download this to fix your CrossFire issue if you have xfire

10.10c hotlist.

• OpenGL 4.1 beta support
  
• Support for the new Morphological Anti-Aliasing feature
  
• Dead Rising 2 – Crossfire profile (Resolves negative scaling)
  
• Crossfire Performance Improvement for:
  
  • Metro 2033
    
  • F1 2011 - (Direct X9 version)
    
  • Fallout New Vegas
  
  
• Performance optimizations for systems with an AMD Radeon? HD 6870 and AMD Radeon HD 6850 series of graphics products installed
  
  • Aliens versus Predator performance enhancements
    
  • Star Craft 2 performance enhancements
    
  • OpenGL performance enhancements – gains can be seen in Prey, Quake Wars: Enemy Territories, and Heaven v2

Here is the hotfix http://support.amd.com/us/kbarticles/Pages/GPU86AMDCat1010cHotfix.aspx