Now finally I have managed to get hold of 5 x Sapphire RX 580 Nitro gpu:s and I have flashed them with new bios. Maybe I will buy one more gpu.
One thing I have realised is that depending on which memory it is on the gpu it can vary pretty much on how much hashrate you can get from the card. Even though I have 5 exakt same cards it is all random which kind of memory you get on the card. My first card I bought I got Samsung memory on and it performs about 20% higher hashrate then my 4 other cards which have Hynix memory. I'm not sure though if maybe it's possible to get higher hashrates on the Hynix memory cards, right now I have same overclock settings on all 5 gpu:s. Maybe I can find better timings for the Hynix cards so they can perform a little better then now. But hashrate is not everything I don't want to overclock too much so the gpu draw gets too high.
Out of the box each card had about 640h/s when mining ETN (cryptonight) after flashing bios and overclocking and undervolting. 4 of the cards have now a hashrate at about 840h/s and 1 at about 1040h/s. And the gpu draw is about 72w for the 4 Hynix cards and about 82w for the Samsung card. And about 4325h/s in total.
If you have suggestions on how I can get higher hashrate on the Hynix cards or if you have any other suggestions feel free to comment. Maybe you have the exact same card with Hynix memory and want's to share your settings.
