As you can see below the Nvidia GeForce GTX 590 and AMD Radeon HD 6990 trade blows across our benchmarking suite.
Almost every other result sees a different winner.
It's also interesting to see how the top two single-GPU cards from the two manufacturers fare when paired up against the two dual-GPU cards.
The GTX 580 in SLI is an impressive beast, though rather pricey, but it's the performance of the Radeon HD 6970 in CrossFire that takes the plaudits.
You may need a chunky chassis to fit them both in, but for the same price as the dual-GPU cards you can buy two of these cards and get faster results. An impressive pairing.
All the results are taken at 2560x1600 at the highest settings with 4x antialiasing.
DirectX 11 tessellation performance
DirectX 11 gaming performance
DirectX 10 gaming performance