It's clearly a balancing act, choosing which of those two strategies you pursue to minimise power draw, and if all four cores are going flat out - which assumes that each one's HyperThreading-enable virtual second core is in use too - the thermal limit will be hit and there'll be no jump beyond the baseline clock frequency.
Intel's widget shows the level of overclocking
The use of Turbo Boost tech might seem to imply that single-threaded apps are better since they run at higher clock speeds, but four cores operating simultaneously at 2-2.26GHz should deliver better performance overall than a single core at 3.2GHz. Intel wants no let-up in software developers' efforts to exploit opportunities for parallelism within their code and create apps that spawn multiple threads.
Run the same 1080p HD video conversion on a 2.3GHz Core 2 Duo T2700 and on a laptop with a 1.3-2.8GHz i7-720QM, says Intel, and the latter will be done in 38 minutes. The first system will take more than two-and-a-quarter hours: 137 minutes, roughly 3.6 times as long.
That's not just Turbo Boost, HyperThreading and the extra two physical cores, mind - having access to faster, 1333MHz DDR 3 memory and 8MB of shared L3 cache plays its part too.
And for all the talk of "intelligent performance" from marketing types, Turbo Boost is really about power conservation. Increasing performance is HyperThreading's job, by maximising the scope for running tasks at the same time. Turbo Boost, where it can, helps those tasks complete more quickly. The sooner a task is done, the sooner a core can tell the OS it's finished and the operating system can, using established SpeedStep technology, tell it to go to sleep for a while.
Performance boost: how faster Intel claims Nehalem is over previous chips
Click for a full-size chart
The whole approach is to get the CPU back to idle as soon as possible without penalising performance when it's needed. Which is why it'll pay off when the notebook is connected to its AC adaptor, ensuring the CPU cores aren't going flat out all the time and so conserving energy whether it comes from the battery or for the mains.
Its all in the leakage...
Modern <=90nm silicon processes no longer lose most of their energy in switching gates (more is the pity) but in simple leakage across the transistors. This exponentially increases as things are made smaller and exponentially increases with temperature. The energy loss happens even if the gates are "idle"!
Fast logic transistors == horrible leakage
So to solve this problem engineers add header and footer power switch transistors (bad logic transistors, so slow) to turn "hard off" whole sections of circuit. This Intel strategy means Intel can have its cake and eat it too.
Running some cores faster and turning "hard off" others saves all that lovely "idle" leakage. The thermal mass of the packaging and die will prevent excessive temperature rises in that one core saving exponential thermal effects.
RE: Physical cores vs. Virtual (hyperthread) cores #
If Windows sucks because it is just now releasing an OS that differentiates between physical and virtual cores, where does that leave Mac? The article handed you a pro-Linux talking point on a silver platter. Did you miss the preceding paragraph about Apple’s grand central dispatch? If your thinking was less Microsoft-centric your OS of choice might be taken more seriously.
Sounds more like they underclock under normal circumstances and return to normal speed when needed.
The turbo boost sounds more like a marketing gimmick to me - 'slows down to cool down' won't sell as many chips!
It very much depends on use case & how well the power is managed. If you double the clock & run for half the time then yes energy used is same or greater (depending on voltage) but, with good power managment, if you run fast there is more opportunity to sleep longer & deeper.
OK, I'll bite
Where do you get that overclock widget?