On my Sapphire RX580s (Hynix) I get 850-880. The same cards with Samsung memory get 980-1000 H/s. I didn't believe it the first time I saw it, but both my Sapphire gpus with samsung are running this speed (1280/2100). I also have an MSI Gaming X+ gpu with Samsung memory that gets the same 1000 H/s speed. Stable with no issues.

On Ethereum, the same cards are running 31.0-31.2 while the Hynix cards are running 31.8 all day long without too much effort.

The Samsung memory seems to be great for CryptoNight, while the Hynix likes Ethash better.