I've tried to improve my mining speed, so I made new rom for RX 480 Nitro 4G with shitty Hynix memory. I was able to reach almost 29MH/s with draw around 80W. I might try to get a little more from this card but there probably isn´t much room for improvements.
WattTool profile: https://drive.google.com/file/d/0B-kL1imq8JJzcHR1SldxSjl2RGc/view?usp=sharing
BIOS MD5: F068FEB35C03DFAF60E33B46A1DB60D0
Just make sure to load WattTool profile before mining as bios defaults to 1750 MhZ for MEM and 1306 for Core (with high voltage). Why? Cause I am using this card even for gaming and it is not very stable at 2 GhZ in 3D. Straps from 1500, default mV for memory.
In case of core voltage, I had to use offset feature in WattTool as I was not able to set mV for core (according to GPU-Z monitoring).
I´d be happy to hear your feedback