Overclocking success is based on how well you did in the "chip" or "silicon lottery". The better binned your processor, ie the better the silicon, the better results you will have when overclocking. The better binned your processor is the higher it will overclock at lower voltages. As you overclock you will need to raise to voltage to get higher and higher clock speeds. As the voltage is raised it creates more and more heat. For these reasons no two processors overclock exactly the same and it is impossible for anyone to tell you what the maximum overclock your processor will achieve.
To answer your question, yes is it possible for the FX 8320E to overclock to 4Ghz on the stock cooler, however it isn't really recommended. If your...