First: backup your original bios using atiflash (not GPU-Z). Make sure if you have same memory on both cards (GPU-Z first tab). If not, backup both bioses separately
Second: download this version of polaris bios editor: https://github.com/jaschaknack/PolarisBiosEditor. Open your bios and click "ONE CLICK TIMING PATCH" button. If memory types are different repeat for both bioses.
Third: flash your cards with modded bios (use atiflash of course). Be carefull to flash proper bios for proper card (only if they have different memory types)
Last: set your core clock 1100MHz, memory: 2100MHz. Set voltage to 850-860mV in claymore's dual miner (or -200mV in afterburner/trixx)

You should get 30+ mh/s. If stable (48h+ with no incorrect ETH shares) you can go up to 1150 / 2150 (core/mem).

Cheers