As long as it is quality 1000w will be fine. For that level of SLi, a 80 Plus Certified is a minimum with Bronze, Gold and Silver being better. Use only trusted brands such as Antec, Corsair, Silverstone, XFX, or Seasonic.
For a system using two GeForce GTX 580 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 900 Watt or greater power supply that has a combined +12 Volt continuous current rating of 62 Amps or greater and that has at least two 6-pin and two 8-pin PCI Express supplementary power connectors.
The Corsair Professional Series HX1000W (CMPSU-1000HX), with its combined +12 Volt continuous current rating of 80 Amps and two 6-pin and four (6+2)-pin PCI Express supplementary power connectors, is sufficient for your system configuration.
Total Power Supply Wattage is NOT a crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.