It is possible to fix your AMD RX470/480/570/580 GPU’s from losing speed every single Epoch if they are mining Ethereum, as the DAG file gets bigger and bigger. A new official driver beta release permits this, and it works quite well. The procedure is as follows:
Use the latest DDU version to remove your drivers in safe mode
Install the New AMD Drivers (beta for blockchain compute)
Install the latest Beta MSI afterburner v.16 from guru3d
You may notice a change in power consumption, and you can adjust your voltage or clocks to compensate. A 6 GPU rig will gain about 10mhs !