The PSU W requirements would be based on peak requirements of each components added together wouldn't it? I am building a SLI desktop and the current power supply I am considering is only 630W.
Current Components I am planning on using:
XION XON-630P12N 630W ATX12V SLI Ready
2x Seagate Barracuda 7200.11 500GB 7200 RPM 32MB
2x BFG GeForce 9500 GT 1GB 128-bit PCI Express 2.0 - 350W PCI Express-compliant system power supply with a combined 12V current rating of 18A or more
AMD Phenom 9850 BLACK EDITION 2.5GHz - 1.20/1.25/1.30V 125W Thermal Power
MSI AM2+/AM2 NVIDIA nForce 750a SLI ATX AMD
OCZ Reaper HPC (2 x 2GB) SDRAM DDR2 1066 - 2.1v
COOLER MASTER 92mm Hyper TX2 CPU Cooler
Current Components I am planning on using:
XION XON-630P12N 630W ATX12V SLI Ready
2x Seagate Barracuda 7200.11 500GB 7200 RPM 32MB
2x BFG GeForce 9500 GT 1GB 128-bit PCI Express 2.0 - 350W PCI Express-compliant system power supply with a combined 12V current rating of 18A or more
AMD Phenom 9850 BLACK EDITION 2.5GHz - 1.20/1.25/1.30V 125W Thermal Power
MSI AM2+/AM2 NVIDIA nForce 750a SLI ATX AMD
OCZ Reaper HPC (2 x 2GB) SDRAM DDR2 1066 - 2.1v
COOLER MASTER 92mm Hyper TX2 CPU Cooler