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I have an i7-2700k that 'auto' overclocks to 4.8Ghz (@ 1.38v)when the CPU ramps up, otherwise it idles at 1.6Ghz(@.96v). My system does this via BIOS where the Turbo capabilities of the chip kick on the extra frequency and likewise voltage to do so.
Normal operations of the Sandy Bridge chips run the voltage from .96v at C-state to 'normal' speed at 1.12v to 1.2v-ish depending on model.
The key to a succesful overclock is to keep your voltage as low as you can, therefore you can get by with as little extra cooling (extra volts = extra heat).
If you're already on the edge of heat stress, the first thing it sounds like you need is a new CPU cooler. They are easy to install, but may require removing the motherboard for a backplate. If you're handy with a screwdriver, you should be able to handle it. There are plenty of good coolers out there for 'standard' overclocks.
Personally, I have watercooling throughout my case - actually the case I built is made out of radiator material to cool the CPU and video card, but I only went to that extreme because the system is completely silent. You should be able to get away with an air cooler that fits your budget, quietness and performance. Here is a table of quiet coolers and their effectiveness: http://www.silentpcreview.com/article1289-page7.html
Although, I'm unfamiliar with the Asus motherboard and bios (mine is MSI), but this site seems to have a handle on its capabilities and how to overclock: http://www.overclock.net/t/1012874/the-official-asus-p8p67-p8z68-p8z68-gen3-series-owners-club
What I don't know (didn't read all articles) is if you can successfully use the turbo feature of the CPU to push the overclock and therefore have a dynamic voltage. The other way to get higher overclocks is to lock the voltage higher than the system will go automatically, but at the expense of always running hotter. But with the right cooler, either is an acceptable method to get more out of your system.