Many people thought that with the better power regulation and better power efficiency that there would be a lot more overclocking headroom with Haswell processor’s but that just simply is not the case. Just like Ivy Bridge overclocking is limited, especially considering what type of cooling solution you have.
We are using an Asetek watercooler on our test bench, which enabled us to achieve a stable overclock to 4.8 GHz with a CPU core voltage of 1.3V. Our thermals were still quite high.
I would not really suggest running an overclock this high for an extended period of time. Most people should be able to run a steady overclock around 4.3-4.6 GHz depending on their cooling setup.