Are you overclocking correctly? i.e. Stress-Testing between changing your clockspeeds and voltages? Something about the way you worded that suggests to me that you're not.
You'll be limited by at least 2 factors - temperatures and voltages. The official max temperature for the FX series is 62c on the core and 70c on the socket. CPU voltage should never exceed 1.5v. As long as you keep those 2 factors in check you should be able to go as far as you like.
Here's a guide that should tell you how to correctly overclock, if you're not sure how:
http://www.overclock.net/t/1348623/amd-bulldozer-and-piledriver-overclocking-guide-asus-motherboard It's intended for asus motherboards, but the same concepts apply universally.