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Based on your specs, anything about 600 watts should do it. I'm running a quad core intel, with 8gb's of ram, an SSD, a single 1TB mechanical drive, and a GTX 570 on a Corsair HX620 and it's just fine.
System Manufacturer/Model Number Self-Built in July 2009 OS Windows 7 Ultimate x64 CPU Intel Q9550 2.83Ghz OC'd to 3.40Ghz Motherboard Gigabyte GA-EP45-UD3R rev. 1.1, F12 BIOS Memory 8GB G.Skill PI DDR2-800, 4-4-4-12 timings Graphics Card EVGA 1280MB Nvidia GeForce GTX570 Sound Card Realtek ALC899A 8 channel onboard audio Monitor(s) Displays 23" Acer x233H Screen Resolution 1920x1080
Keyboard ABS M1 Mechanical Mouse Logitech G9 Laser Mouse PSU Corsair 620HX modular Case Antec P182 Cooling stock Hard Drives Intel X25-M 80GB Gen 2 SSD
Western Digital 1TB Caviar Black, 32MB cache. WD1001FALS Internet Speed 15/2 cable modem Other Info Windows and Linux enthusiast. Logitech G35 Headset.