VR Zone claims NVIDIA's upcoming GeForce GTX 580 will have a TDP of 244W, slightly less than the 250W of the GeForce GTX 480. Additionally, the site also found some benchmark results and claims the (paper)launch may be as soon as November 8/9th.
The benchmarks show an average improvement of ~17% for the GTX 580 over the GTX 480. The maximum increase is in 3D Mark Vantage - ~35%, while the minimum increase is in Resident Evil 5 ~5%. Against the Radeon HD 5870, the GTX 580 wins comfortably by an average of ~45%. The gaps are massive (~2x) in tessellation oriented benchmarks, building on GTX 480's strengths, while the DX10 benchmarks narrow the gap considerably. Unfortunately, according to these benchmarks, the GTX 580 will end up slower than AMD's previous-gen Radeon HD 5970, on average, let alone AMD's upcoming flagship - Antilles / Radeon HD 6990. GTX 580 against Cayman / Radeon HD 6950/70 is the real battle here. Naturally, we would advise you to take any such leaks with a grain of salt.