You should be able to get 28-32 mhs even on a rx 480 sapphire nitro.

Download your bios with atiflash, open it in polaris bios editor.

Copy the memory timing for the 1500 or 1750mhz to the 2000 mhz and higher blocks.

I believe you can copy 1500mhz memory timing code to 1750 and 2000 blocks.

Make sure you backup original bios first.