Sapphire seems to sell two versions of their Nitro+ RX 590. One will boost to the common advertised speeds of 1560/2100 MHz and one version won't tho they are named exactly the
SAPPHIRE NITRO+ RX590 AMD50 Gold Edition Now Available
SAPPHIRE RX 590 8GB Graphics Cards GPU Radeon RX590 GME 8GB Nitro AMD Video Card Desktop PC Screen Computer Game Map
AMD Sapphire RX 590 Nitro+ SE 8GB Review | KitGuru- Part 3