Mattthev does not seemed to be too exited to develop a RX 580 bios mod specific for GGS.
So I need to do it myself following his tutorials.
Currently I have modded my the bios with the UberMix 3.1 timing strap copied to 1:2000 only.
Cryptonight hashrate went down from 1070 h/s to 1057 h/s and is using 990W of the wall.
core clock = 1300, memory = 2000, voltage untouched
So far, running stable for 30 minutes.

UberMix 3.1 seems to be the mod most people are using for RX4xx/RX5xx cards.
Would you agree or does anybody have other recommendations?