Various RX 580s 8gb sapphire nitro has best cooling according to me. All other brands fan is failing after 3 years of runtime :-)
Each card separately fine tuned (could do more) :-)
Avg setting 1180 core @840mv , mem 2100@850mv using claymore with straps 1,2 rxboost 1 -y ....
I get average 32.x mhs @ 135watts on each gpu(miner shows 85watts average), could make it more efficient but dont want to reduce hadhrate as have fixed power rate :-)

6 gpu rig total : 196mhs@850watts off wall. . Claymore shows 540 watts gpu consumption lol, i wish :-)