I'm using the latest drivers but with compute mode enabled. Only getting ~24.6mh/s on each card. Thats at stock 1306mhz gpu & 1750mhz mem.
How are you getting ~29mh/s?
You need to mod the VBIOS with different memory timings and also overclock the memory. You can downclock and undervolt the core to save power as well.
Generally speaking the memory can go to 2000 - 2200 MHz depending on which ICs are used and their quality. Core can be downclocked to around 1150 MHz and undervolted to 800 - 950mV without losing hash rate. You will have to do stability testing to figure out optimal settings for your cards as each one is different.
You can use this version of PBE to do an easy timings mod:
https://github.com/jaschaknack/PolarisBiosEditorBack up your original and flash the modded one with atiflash:
https://www.techpowerup.com/download/ati-atiflash/You may need to disable the driver's VBIOS signature check after modding. Use this tool:
https://www.monitortests.com/forum/Thread-AMD-ATI-Pixel-Clock-Patcher