Our three sample systems show that few if any people actually need anything more than 850W power supply, especially if you can get an appropriate number of connectors. About the only reason you should consider anything more is if you want to keep your power supply at a lower load, since optimal efficiency and lower noise levels usually come at around half the rated output. Overclockers might also want a bit of extra headroom. Otherwise, there's really no need for a 1000W power supplies, and certainly not those with even higher ratings.
Our power supply reviews include efficiency and noise level charts at various wattage loads. Using these, you can easily compare your own system to see what sort of efficiency and noise you would get. You might be surprised to learn that your intended high-end setup really won't make much use of that spiffy new 1000W PSU; you might be greener than you think!
AnandTech: Debunking Power Supply Myths