Actually, while "High Performance" mode does not actually over-clock the processor, it does prevent it from dropping into lower clock speeds or sleep states. As a result, certain benchmarks return higher results, such as Mathematica.
In High Performace mode, Mathematica places a G53SX with i7-2630QM at 0.98-0.99, which is just behind a 3.06 GHz i7-920
desktop. Under other performance profiles, the numbers drop to about 0.94-0.95 or less, which is about on par with a high-end 1st-gen i5 desktop processor.
If you are worried about burn-out, don't worry. ASUS builds the best cooling solutions, so over-heating is not a concern. Lots of other companies skimp on the cooling, and when the work load increases, it shows. That stealth-fighter design isn't just a stylish design, it allows the engineers at ASUS to put in a much better cooling solution.
High-performance modes would be an issue on a macbook pro, where Apple puts a comparable processor in with only one tiny fan:mad:. I have my ASUS G53SX up on a cooler, but it doesn't help all that much, considering that ASUS ROG computers draw air in under the speaker grill:), as opposed to the bottom of the notebook like most manufacturers.
If heat is a concern, buy a decent quality cooler, they aren't that expensive. One might call them a cheap peace-of-mind insurance policy for the careful. Alternately, run the system in "Entertainment" mode, which allows the processor to sleep, but will run at full capacity when the need arises. Personally, I use the "Quiet Office" profile because it runs the fans less. Not that the fans are usually that loud, but more sleeping=cooler processor=more peace of mind;).
Hope this helps!