A couple of days ago Anandtech took a look at three very high-end power supplies: the PC Power & Cooling Turbo Cool 1200W, Cooler Master Real Power Pro 1250W and Tagan ITZ 1300W PSU.
One reason such requirements are overkill is that the resolution you are running is largely responsible for higher GPU requirements, which in turn leads to more power hungry systems. If you are running a top-end video card (or two) at just 1280x1024, much of the performance potential is going to waste. Still, multiple GPUs under load will still require a beefy PSU, generally starting at 400W and going up from there, depending on the rest of the system. If you're running a 30" LCD on the other hand - particularly with overclocking - we have seen power requirements break 600W in worst-case scenarios.
For those people who still believe the marketing hype - or for the extremely rare exceptions where you might actually run a system that needs 800W or more of power on a regular basis (feel free to let us know what you're doing that requires that much power!) - if you're thinking about buying this kind of power supply we are presenting today three of the highest rated power supplies on the market.
Check it out over here. The reviewer doesn't really tell you which PSU from these three models is the best one - he says they are all a very good choice if you really need a lot of power for your rig.