The performance boost over the GTX 460 is an impressive 30% almost across the board. Sometimes it's slightly higher and sometimes it's a little under, but for the most part it's pretty consistent with Nvidia's marketing spiel.
The overclocking performance is mighty good too, delivering in excess of a 10% increase especially in the DirectX 11 games.
The trouble is the Radeon HD 6950 has become the card of the moment. A combination of price drop and BIOS flashing has created an AMD card that is more desirable than anything we've seen out of the red team in a long while.
DirectX 11 tessellation performance
DirectX 11 gaming performance
DirectX 10 gaming performance