I recommend staying below 1.4v, will your CPU spontaneously die because you went slightly over it? No, but it will cause problems in the long run. Also you are going to want to ignore other people's results and get a feel for your individual processor. I can get my E6750 to boot to windows @ 4.0 Ghz, does that mean it can open up firefox without a BSOD? No, but I have a feel for my processor. To be honest, the normal 24/7 overclock on that processor is about 3.8 GHz, but 4 GHz is supposed to be pretty easy with the 125w version. Also remember people are dishonest, stupid, and ego-centric so don't pay too much attention to their results.
First, disable all thermal or power throttling features, cool n' quiet to be exact. Also read a guide about overclocking on that CPU and MB if possible. Remember, put everything to stock and overclock 5 MHz at a time. When it won't boot into windows mess with the settings a bit (look up a guide on which) to see if you can manage it, remember you want to learn just what the max clock is that you can push and then worry about the multiplier. If not, start increasing the voltage by the SMALLEST possible increments until you reach either 3.8-4.0 GHz, 1.4v, or a point where you are happy. Either way, at this point start stress testing. I recommend 2 hours of small packets and 8-12 hours of mixed packets in Prime95. Once you mess with your settings to get a decent overclock of either 4.0 GHz, whatever is stable at 1.4v, or whatever makes you happy and can do said Prime95 test without errors, start benchmarking games and other apps. Do some random CPU intensive stuff, like video converting. If everything is still working well then congratulations, you've overclocked your processor.
OVERCLOCKING TAKES TIME PATIENTS AND COMMON SENSE. It SHOULD take days, if not WEEKS. Remember to stay with-in AMD's specs, DO NOT GO OVER 65c, if it is reaching higher then you need to lower the clocks/voltage or get better cooling. I recommend using the system for a day or more and making sure that everything is stable BEFORE you start overclocking.
I know overclocking sounds fun and exciting, and it is, but it is also hard work and time. Also I realize that you may have overclocked before, and if this is too simplistic I apologize, but it really takes a lot of knowledge and practice until you can get to the point where you treat an overclock like it ISN'T your first, I'm not quite there yet myself.