rx570 near 29 30mh just crashing
with my msi rx570 8gb i get 30.5 Mh / s with phoenixMiner and claymore 31.6 Mh / s
If you will use AMD Memory tweak tool to set REF parameter you will receive speed on PM more than on CM.
how much should I set it
It's easy. Download tool -
https://bitcointalk.org/index.php?topic=5123724.0Start mining. During mining launch the tool. On the bottom of the each GPU tabs you'll see parameter REF. It 5 on default for polaris cards. Set it to 20 for each card and apply be pressing button in the right bottom.
Look into miner - speed will increase. Test for some time. If it will no hardware errors - try to set REF 30, test and so on.
Max REF for each card is individual. Some can normal work at 60-70, some starts to give hardware errors on 25.