Obviously, just because we can push 4Ghz on a D0 stepping i7 920 doesn't mean we should.
I recently saw a very interesting benchmark discussing an often overlooked aspect of overclocking. Most of us will think in terms of pure performance, or performance vs temperature and the need for expensive aftermarket coolers, because that cost might cover the price difference towards the next bigger CPU in the product line, defeating the purpose of overclocking in the first place.
However, not a lot of people think about performance gain vs watts expended. Granted, this is not an issue if you only use your PC at certain times of the day and it also depends on how expensive electricity is where you live, but some people keep their PCs open for days, weeks, or months on end for a variety of reasons.
For example, i have a sibling studying abroad on a post-graduate program and while i do have a combined internet and telephony package at home with free calls to landlines in most of Europe, this doesn't apply to my relative's landline should they need to place call. So, since one of the cheapest and easiest ways for them to communicate is skype, my PC is almost always on to receive incoming video calls.
It might seem like small fries but it's not, in fact some guys in a local hardware forum sat down and measured the average power consumption of a mid range PC. It turns out that if you keep it on 24/7, the way electricity is priced here it translates to an extra 50-70 Euros or more on the bills every couple of months.
In that sense, when overclocking it might be also useful to think about performance vs watts expended because that drives up the bills. On a recent article i saw (excuse me but i don't remember where, as i don't usually spend much time on dedicated hardware websites unless i'm doing some research prior to buying new components), it was deduced through a series of benchmarks under various load conditions that the best compromise is around the 3.6Ghz mark for an i7 920. Higher than that and the extra performance is not enough to justify the cost of the electricity used.
Just something extra to keep in mind in case you might be interested
