--xintensity 60 is good on the rx 580. ppl got it working in hiveos after upgrading to the latest image.
And the winner is --xintensity 284
I did a 3hour * 4 test last night on 2miners.com on the same card. rtx 2060 mobile
--xintensity 1024 32.54 mhash (pool less than 30)
--xintensity 2048 32.56 mhash (pool 34++)
--xintensity 3078 32.58 mhash (pool less than 30)
--xintensity 4096 32.60 mhash (pool 38++)
3 hours on each intensity is not a long enough test, but 4096 was still the winner on this pool for NVIDIA... If you compare the local speed to the default (--xintensity 284) you get a +1% speedup. The test had no stales or rejected shares poolside.
It does not take 3 hours to get reliable information about pool hashrate, at least 24 hours