Well I have the same processor and let me tell you every chip is not the same. Some can use a lower voltage for overclocks compared to others. I myself have my Phenom 955 at 4 ghz with the Kuhler 620. If you are thinking of overclocking on the stock cooler I would strongly advise you not to do so. I myself see a noticeable difference in games with the overclock. In addition, I would say it's the CPU cooler that matters in temperatures for the CPU, not so much of case fans (though you do need some). Also to be on the safe side do not let temperatures exceed 60 when under load.
Edit: If it helps my voltage is 1.45 @ 4ghz. I recommend disabling Cool'n'Quiet if overclocking.
Also here is a wonderful guide created by a mod (4Ryan6): http://www.tomshardware.com/forum/274820-29-black-edition-overclock-raising-multiplier-guide
I learned to overclock my processor by reading that.