For the ones that still have problems with overclocking / reducing voltage with the block chain drivers and Claymore 9.8 you should check OverdriveNTool - tool for AMD Polaris GPUs.

I know the tool have been already introduced here by another users, but for the one that still have doubts I want to confirm it again.

example: RX 580 8GB Special Edition 8GB Hynix (The blue one)

1200 Mhz/ 2200 memory with 900 mv / cv
ETH 30.747 Mh/s with SiaCoin at 614.935 Mh/s at maxim 105/110 watts

You should build a batch script or include in the miner batch a loading of the profile, like that every time the miner start it applies the overclock profile.

Example:
start /d "C:\Users\RIG-XX\Desktop\OD" OverdriveNTool.exe -p03"3a" -p04"4a" -p05"5a" -p07"7a" -p08"8a" -p11"11a" -p12"12a"
exit