For a long time i was running my 570 + 480 with times around 10-11 minutes per WU. After changing to stock app 1.39 the times are going up to 15+ minutes and the gpu-load is down to 50-70% from 99% before.
BM is 6.12.22, OS Win 7 64, driver 266.58
And please do not suggest me to update the drivers to 270.xx . After i had done the Gpuclock went down from 800 to 450 after some times. Its a buggy one
Think i found the problem. Yesterday i fired up 5 vm's . Did'nt see that they are at priority level "normal". The GPU threads are at the same level, so they wont get the needed power from cpu. After reverting the VM threads to low the Wu times were geting back to normal.