Recently it became apparent that the Radeon HD 6950 in fact is a 6970 with shader processor clusters disabled. You'll need to re-flash your card though. You can perform the flashing process from within Windows and het, thanks to AMD's new Dual-BIOS feature if something would go wrong, you can switch back. We successfully tested an unlock on a HD 6950 cards. Other have tried one AMD engineering sample, one HIS media sample and one ASUS retail card. All of them unlocked perfectly and run at HD 6970 speeds now. Your graphics card needs to be a reference design sample.

 The Download & instructions are courtesy of TechPowerup!

1. Grab ATI Winflash from here (32 & 64-bit).
2. Download HD 6970 BIOS. The Sapphire one I linked to will work on all reference design cards from any vendor.
3. Make sure the BIOS switch on the card is set to the 1 position (pictured further down if you don't know where it is).
4. Run ATI Winflash, click Save to save your BIOS, so you have a backup in case something goes wrong.
5. Load the HD 6970 BIOS into Winflash by clicking Load Image, followed by Program.
6. Let the flashing process complete and reboot your system.
7. Check the shader count using GPU-Z, it should show 1536. Make sure you use the linked version of GPU-Z, the official 0.4.9 version does not support HD 6900 Series properly. If you see a shader count of 1600, your GPU-Z version is outdated and you should get the one from the link here.
8. To ensure maximized performance open Catalyst Control Center, go to the Overdrive tab and set the PowerTune slider to the +20% setting. The "Testing" section of this article has more data on that.
9. Check stability in Windows desktop applications and games.

If you get an error like ID mismatch or Could not erase ROM, then you'll have to do some extra work in a Windows command prompt (or DOS): Run atiwinflash -unlockrom 0 followed by atiwinflash -f -p 0 bios.bin where bios.bin is the path and filename of the HD 6970 BIOS you downloaded.

More info discussion  Click here. Mind you that flashing a BIOS can always be tricky, you do so at your own risk.