I'm interested too. However it seems that this time the 4GB version has 2000 MHz Memory, so it's probably Samsung memory.
As far as I'm aware of, most RX480 4GB came with Hynix memory. Those with Samsung memory like mine could easily be overclocked from 1750 MHz to 2000 MHz and beyond. Mine is 100% stable at 2120 MHz memory clock.
On the other hand, at 1411 Mhz core, I don't think my card would be stable at default voltage, unless some BIOS changes with the RX580 also improve stability (I would like to test that).