Depends heavily on the chip. Each chip is different and just because one guy can hold 4.5Ghz doesn't mean the next guy will with the same equipment. However, here's how it works in a very basic point of view.
You boost the clock (with multiplier settings on a K-Series) and get a higher frequency. At a certain point the voltage (only if not set to auto) will need to be increased to preserve stability as the higher the clock the higher the possibility of instability.
Now the worst part, higher voltages can cause more degradation of the CPU itself along with heat it can severely lower the overall lifespan of the CPU. However most low overvolts won't effect it's usable lifespan as by the time it fails you would have upgraded a couple of times. However, this can actually be completely the opposite as some chips react different to voltage. I've heard of guys frying their Ivy Bridge chips at as little as 1.375v for only a couple weeks. While I've also heard of guys running 24/7 for quite a while at even higher. So the risk is in your court with the voltage settings. Personally I don't let my Sandy Bridge go over 1.3v often and if I had an Ivy I'd probably have that limit set to 1.25v or lower.
However out of the average, if you applied the thermal paste correctly, learn about voltage setup, and know how to test for true instability... I'd estimate you could get 4.5Ghz out of that chip with decent temperatures while staying within a decent voltage.