It's not my goal to get into the details, this article is more intended as a brief overview of some reviews to to discover if AMD's Radeon HD 6900 series is worth its salt. First we head over to AnandTech, they conclude the performance of the Radeon HD 6970 is more or less equal to the GeForce GTX 570. The 6970 is $20 more expensive than the GTX 570, but it uses about 21W less in load and runs a bit less noisy in load. The Radeon HD 6950 on the other hand delivers about 85-90% of the performance of the Radeon HD 6970 for $70 less. It's about 7-10 percent faster than the Radeon HD 5870 but costs around 20 percent more.
For a second opinion we check out The Tech Report's review, they also write it's nearly a draw between the Radeon HD 6970 and GeForce GTX 570. They found the GeForce GTX 570 draws less power and generates less noise under load, but point out that the Radeon HD 6970 has the advantage of extra RAM and the support for three or more displays from a single card. The Radeon HD 6950 is described as an ideal stepup over the Radeon HD 6870.
Another review can be found at Legit Reviews. This site also found that the performance of the GeForce GTX 570 and Radeon HD 6970 is quite similar. Both cards bring new features and better performance to the table at a price point that is competitive with NVIDIA's GeForce GTX 500 series, Legit Reviews writes, but both cards are a bit power hungry. The reviewer complains the cards hit 95°C in games on the open test bench and that they're quite loud in some of the games when running in CrossFire mode.