Now on to the second variable in our efficiency calculation: power.
The differences you see each step of the way relate to the voltage needed to keep our Core i7-3960X stable. We were able to use Intel's default voltage setting at up to 4.5 GHz. But once we needed an offset, the idle power started creeping up. By the time all six cores were running at 4.7 GHz, we were seeing questionable performance gains, but bigger power use.
The scale doesn't look that much more alarming under load, but the numbers speak for themselves. Power consumption increases based on frequency, and then our voltage alterations exacerbate the end result. Once you're pushing 4.7 GHz in lightly-threaded apps (and 4.5 GHz in workloads that tax the whole CPU), system power exceeds 300 W. That's not even taking into account graphics power, since only our processor is subjected to a load.
Nice to know Intel doesn't just set the stock clock speed for just performance!
Did someone at Intel tell you that was the reason for a lower Turbo Boost limit, or did you just assume it?
I think we should be careful of this kind of guess at another person's, or company's, reasoning. There could be some other cause for the limit - for example, they will obviously sell it for a lower price, so wouldn't a possible reason be they have looser binning specs to allow for chips that wouldn't make it under more strenuous tests through? (Remember, Intel, or any CPU manufacturer, doesn't warrant the product based on what it can be pushed to, and is generally going to provide it at a clock rate they feel is safe over time to guarantee.)
I'm certainly not saying it is a bad assumption, what you said makes sense to me, but I do think there are enough other reasonable possibilities that I wouldn't have stated it as a fact unless I knew it to be.
I do think articles like this are very important; those of us who overclock, especially when we turn off all the power-saving features in hopes of reaching that max stable a CPU can do, should be aware of how much money we are spending if we keep said OC. It's more than just the high end cooling solution.
The people that bash higher capacity PSUs could also stand to learn a thing or two, here. An overclocked CPU can require a huge amount of peak power over and above what a stock CPU needs (349W measured here). An overclocked Sandy Bridge-E and an overclocked GTX 580 could require a peak power of 650W just considering those 2 components!
A Kill A Watt or similar device is a great way to measure how much you actually spend a month operating your computer. You might be surprised.
Tom's Parallel Universe Hardware.