http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-4.html
Read that page, it explains it well.
GHz speed is not the only thing that matters. And if you keep the 4770K cool, then it runs @ 3.9GHz.
I am guessing you want to build a gaming PC?
If you give us your budget, games you want to play and where you are purchasing from, we can help you a lot easier.