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Just saw your post, I get it that you were using stock bios cards with Claymore and applying straps and rxboost to increase the hashrate. AFAIK Phoenix miner currently does not support "straps" for RX580 (all polaris) cards, so you'll have to bios mod these cards manually (using 1 click bios mods or any other tools) and then try using the overdriventool settings and then you'll get similar hash rates on RX580s.
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Thank you for the reply.
OK. I’ll reflash them again to mod BIOS.
Can you remember if I need to run the AMD Patcher tool after?

I’ll report back as soon as it’s done.