Try dropping your AGGRESSION to 8 or below.
Also I found that poclbm was more stable and ran cooler for own three rigs having six overclocked 5770s running at 60-70 C.
Yes, You are right. Overclocked to 960/600 XFXs 5770 with 100% fan speed, temperature is 63-65 C. Two 120mm fans blowing air through case.