Benchmark: DiRT 2
DiRT 2, a lovely-looking racer and one of the first games to use a DX11 path offers improved visuals whilst burning through the London map.
DirectX 11 title Colin McRae: Dirt 2 sums it up nicely. You're paying an up-front premium, but you are getting more bang for your buck.
In certain scenarios, you can expect to see Radeon HD 5850 and GeForce GTX 470-beating performance.