The Core i7-5960X has an unlocked clock multiplier, which means you can overclock it by simply changing the core multiplier.

We were only able to tun it stable at 3.7 GHz, mantaining the cache memory clock at 3.0 GHz. At 3.8 GHz, we began to experience random crashes.

However, keep in mind that we did not change voltage or more advanced options, so with a little more patience, you will be able to reach higher overclocking levels.