According to FudZilla, the GeForce GTX 480 is twice faster than the Radeon HD 5870 in some situations (like in Unigine Heaven benchmark).
But AMD has already the reply to GTX 480: the Radeon HD 5970 with 4GB of graphics memory.
Sapphire is the first to release this kind of card with a custom VG cooler (ouch! three slots height!!), overclocked speeds and 2 x 8-pin PCI-Express power supply connectors.