[citation][nom]Crashman[/nom]No, because the power supply is only outputting 575-600W. Wall power x efficiency = power used by the computer. Peak power consumption of 75% capacity is will within the power supply's "optimal" range.Anything you have to say about low-quality power supplies doesn't apply here as this is a high-end unit. The main reasons it costs less than the same brand's higher-priced units is that it's unpainted and has no removable cables. Soldered-in cables are also more reliable, so one could argue this power unit is out of YOUR league.[/citation]
The article sites higher usage than what you quote and other reviews of two 580s in SlI have listed usage near 700W (I know because I hear your argument all the time in the forum and several professional reviews have been posted which show the actual usage of this system's typical power usage). Even using your figures I disagree with your statement that at 75% the unit will be in its most efficient range.
Before I bought my PSU I read hundreds of PSU reviews and I began to notice that nearly all of the PSUs start to drop in efficiency at 60%. This varies with PSU but it is very consistent. Thus if you spec your PSU to run at 50% capacity you get the best efficiency - and really this cannot be argued. However, you are correct that some PSUs maintain reasonably good efficiency at 75% usage but you are missing other factors.
Because you are pushing the PSU to its upper capacity at 75% (really closer to 85% with real world numbers), it will heat up and switch to high fan which increases noise and lowers efficiency. This in turn heats of the interior of your case.
Real world example, I had an I-7 920 PSU that came with a 520W PSU. I upgraded the GPU to the ATI 5850 and added a Corsair HX 750 (one of the highest rated 750W PSUs on the market). The PSU constantly went to high fan and ran VERY hot. While the HX 750 is a great unit, with high fan on it is distracting and noisy. I really hated it.
Fast forward to my current build. It is a 2600K with an ATI 6950. My current build has two more HDDs, a blu-ray burner, a sound card and the Noctua NH-D14 added to the PSU load that my I-7 920 did NOT have. With this build I got smart and I got the Corsair HX 850 PSU.
WHAT A DIFFERENCE!!!!!! I have never even hear the PSU once, I am not sure that the fan ever turns on. According to the reviews I have read it is running near 92% efficiency most of the time. It NEVER heats up. Now this is REAL-WORLD first-hand experience. Keep in mind also that my second build draws much more power than my first build and the HX 850 handles it with ease.
Thus spec'ing your PSU to run at 50% capacity is a much more intelligent approach and it really doesn't cost that much. I got my HX 850 for $144.
Really for a two 580 SLI build, I think that the AX 1200 is by far the best PSU for a high-end build. This is because it is much more efficient at low capacity usage than comparable 850W - 1000W units - so it will run more efficiently (by far) than an 850W unit. Also it can regularly be bought on sale for $250 and so you don't have to mortgage your house to afford it. Also, it comes with Corair's legendary 7-year warranty. Also keep mind that PSU technology is not changing much and so the AX1200 will not be outdated in 7 years.
Finally it is a myth that soldered cables are more reliable than modular units but even if it was true I would not buy a non-modular unit - they frankly are a tangled mess and are miserable to build with. Poor solder connections are as common as dirt, ask any experienced computer tech. It takes a lot of skill to make a good solder connection.Though you believe a myth, I would take the supposed risk for the ease of using a modular unit. Keep in mind that the best units on the market right now including most Gold-rated PSUs are modular. I think Antec's 1200W unit is the only unit I can think of that is not modular and it is not quite as good as the AX1200 which is fully modular (both are highly rated).
It really never ceases to amaze me how many people run to the cheapest PSU to save $50 even though it will run hotter, be much more noisy, will cost them more for power, will not be as efficient and will not be as stable so it is more likely to damage expensive components. But damn it, if I can save a whole $50-$75 it is worth playing Russian roulette with my $2000 worth of components.