7770 Overclocking Help

Hey guys I got two Black Edition XFX 7770 and I was trying to overclock them. By adjusting the fan speed I've been able to get a stable temperature at roughly 55 degrees but after a set amount of time I still get a crash and revert it back to stock. Anything to help out with this? I'm pretty new to the overclock media and thought this would be a good place to look. What I was able to go up to was 1200 core clock and 1250 memory.

System Specs:
FX-8150
GA-990FXA-UD7
OCZ 1000W Power Supply
16GB Vengeance 1600

What are using to overclock? CCC? I have an XFX 7770 overclocked as well :3

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