I modded mine up to 23 not more
If you have the Samsung memory, like the OP does, make sure you use the August-23 AMD Blockchain drivers.
If you are using that and you have OC-ed the memstraps of your card to use 1500 (also don't forget to decrease voltage) the only thing left to do will be to overclock your memory. For my rx 470s i've found that its safe to OC memory up to and between 1950 and 2000. With this, I get at least 26 MH hash rate.