I get 1040 h/s on my armor rx 580 hynix 8 gb I=55 and 720 h/s only on my nitro+ rx 480 elpida 4 gb I=29.5, I tried different timing straps on the 480, but it didn't change much

One strange thing is that the reported hashrate change each time I restart the miner
(most of the time, it's one time good, with 1040 h/s on the rx-580 and one time "bad" with 930 h/s on the same rx-580... and it makes comparison difficult)