I can't remember where I read this, but it applied to Intel at the time. AMD most likely uses a similar technique.

Let's say the i7 is classified as 3 models:
4700 (3.0GHz)
4725 (3.3GHz)
4750 (3.6GHz)

Intel manufactures in batches, let's say 100 units. The entire batch is tested first at 3.6 GHz. If the batch passes, the chips are labelled as 4650.

If the batch failed at 3.6 GHz, they are tested at 3.3 GHz and labelled as 4625 if they pass. And so on...

This is why some get a chip rated at 3.0 GHz that overclocks just fine at 3.6GHz and some don't.

You're not really overclocking, you're just running the chip at a speed it was designed to operate. You just have to make sure to cool it adequately.

Also, Intel designs with a margin of safety. That's why you can run a chip seemingly beyond their highest model.

Robert