It seems -clkernel 1 option is not working for my rx570/580 4gb. The power consumption on-the-wall is still the same. I also didnt put -gt option in my config.txt
UPDATE:
Try -clkernel 2 and auto-tune gpu again.
And still the same hashrate and power consumption.
The option for lower power consumption is -clgreen 1
It is not clkernel -1
Sorry, my mistake. I get 2-4 watt power reduction with 2 gpu (rx570 and rx580) and no hashrate drop.