cpu overclocking vs. power

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Wattage is as important as signal integrity. You want a nice stable PSU that send a nice and even signal. Cheaper PSUs' typically have poor voltage regulation so the input signal fluctuates a lot, which can make or break a stable overclock.
I switched to this PCPnC PSU mainly for that reason. I had a coolmax 700w PSU and at first it was stable but after a few days the voltage was all over the place and my OC was failing. Then I read a review about it @ www.jonnyguru.com and needless to say that was one of the things that the PSU was seriously lacking.

As for high watt PSUs', yes theyre mainly for peripherals.

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I don't know of one right off hand.... maybe someone else does....

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It's none of my buisiness what size of PSU you go for, but you really don't need a 1KW supply if it's your sig rig your powering. Alright powerful supplies are great if you need them to power demending equipment or when upgrading requires it, but they're expensive bits of kit if all that power it just sitting there doing very little. Just my 1p's worth

You can use psu calculator lite if you want to get a general idea of PSU requirement.

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PSU rule of thumb #1: The wattage is not as important as amperage on the 12v rail. The 12v rail is what both the GPU's and the CPU draw from, so good amperage here is vital.

Rule #2: you CAN NOT simply add amperage across the multiple rails. It doesn't work like that, and alot of people get confused with this (I did too, dont worry). The voltage on the 12v rail is calculated by taking the available wattage on that rails (look at the sticker on the side of your PSU for that), and deviding by the voltage of that rail. For the 12v rail this is obviously 12.

On my Earthwatts 430, I have 360w on the 12v rail, so (360/12)= 30amps.

I'm right at the edge with my current setup and my PSU (mostly due to the OC'd 720 BE that I just added, my brisbane was just fine) I wont add anything else to my system until I get a larger PSU, but so far, even under severe testing (large OC on both the GPU and the CPU) it has held up just fine.

The point is that you dont need a kW PSU, thats all. For single card setups I would usually recommend a PSU with around 35amps (500-600w psu), and for multi card setups I would get at least 40-45amps.

Good luck

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I thought the CPU power was drawn from the 3.3v?

At any rate, with regards to wattage for a given system. I typically like to have a more powerful PSU that well exceeds my rigs needs. If it's only using lets say 50-60% of the PSUs power, it should run more efficiently. With efficiency comes stability as the components such as the voltage regulators dont get as hot and keep the signal stable.

I used an Antec Sp 500w to power my rig w/ 2 9600GSOs' and one of the voltage regulators (the one for the 12v rail) squeals like a stuck pig now. And while stress testing Ive noticed my 12v power drops way down to 11.6v with that PSU.

As for split 12v rails, you get the advertised wattage/amperage but only on 1 rail at a time. So if both rails are being used at any given time the power output is reduced to each rail.

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CPU's used to run off of the 5v or the 3.3v, now it is primarily the 12v rail that powers them (the "new" 4 or 8 pin power connector for the CPU... thats 12v). I think its been since the P4 days or so, but I could be wrong on the timing there.

The ram runs off of the 3.3v as well as some other mobo stuff, while the 5v is used in alot of peripherals (USB runs on the 5.5v).

Also, I'd like to agree with the statement about the "target load" of the PSU. Running a PSU at a low percentage of what it can produce makes it not very efficient, as well as running it at to high of a load.

I personally feel that the "sweet spot" of a PSU should be about 50-70% of the rated output.

Cheers!