I am using PeterL calculating.
I change Thread Concurrency. Shader multiply by 8. So, 2560 x 8 = 20480,
Same Intensity, same gpu hardware config. and no gpu-powertune.

For 1 hours, It seems more stable,
The lowest hashrate goes low min= 700 KH, goes Up max 1.01 MH.
I' ll watch it, and report soon.