I think I will just give it a go and try out the RX 580. If there is no improvement I can just return it.
I know that the Sapphire Pulse RX 580 8GB is the officially supported model by apple. Besides other versions by other brands there is also a reference model with just 1 fan:
Is there any benefit in getting this version? I guess the cooling will be worse with just 1 small fan compared to the 2 large fans on the Sapphire model? On the other side the heat will directly be transferred out of the case so the overall temperature within the Mac may be cooler?
I chose the Sapphire RX580 Nitro+ 8GB mainly because of it's bigger cooler.
Fans are dead quiet, even when playing a game for a few hours...
Maybe the blower style cooler is noisier, but since the heat is transferred outside the mac pro, the PCI compartment fan will be more quiet. No idea wich of both options is less annoying
Got my PSU and PCI fans under control now with Macs Fan Control.