Intel can't overclock their chips, by definition. Overclocking is when you increase the speed above what it is set to from the factory. Intel is the factory. Whatever speed they set a chip to run at, becomes the official speed that overclocking is relative to.
They simply produce a batch of chips, and then they test them to see if they can run safely at the intended speed. If they produce chips that can work reliably at 4GHz, then they sell them as 4GHz chips. if they produce some that can only work at 2.8GHz, then they sell them at that speed.
A CPU doesn't have some kind of "natural" speed. They design the chip with a clear expectation of how fast it should be able to run, then they manufacture it and hope for the best, and finally, after testing, they know what speed it is actually able to run at, and then they configure it to use that speed by default.
So depending on your perspective, Intel either always overclock their chips, or they never do. But they can't overclock more than they do already.