Phoronix posted a review on the Sapphire Radeon HD 6950 running under Ubuntu Linux

Have you been wondering how the AMD Radeon HD 6900 "Cayman" graphics cards are running under Linux? After all, Cayman is quite different from the rest of the Radeon HD 6000 "Northern Island" GPUs and its open-source Linux support came much later. There is no reason to wonder any longer as Sapphire has sent over their Radeon HD 6950 DIRT 3 Special Edition graphics card, which we have now put through our arsenal of tests under Ubuntu Linux.

  Sapphire Radeon HD 6950 Linux Review