Interestingly for those of you who settled for the less expensive variant, it seems that all currently shipping Radeon HD 6950 cards from all manufacturers are just one software tweak away of reaching their full potential, essentially becoming a full-blown Radeon HD 6970. As techPowerUp explains, AMD typically locks down shaders on production cards via on-die fuses or on the GPU substrate, but in this case they’ve done the same simply by reconfiguring the VGA BIOS.
This means you can unlock the additional shaders on the HD 6950 by flashing the card with a HD 6970 BIOS. A detailed guide with everything you need to unlock the card is available here. The process is reported to have been successful with AMD engineering samples, as well as on the HIS and Asus retail versions of the card. Just a few words of caution though: be sure to back up your existing BIOS before you play with it and know that you may be voiding your warranty.