You can get 28/29 hash rate from a Micron memory RX470 using the following modded BIOS settings without the need of wattool (but it helps):

Def GPU Clock: 1144 Mhz
Def Memory Clock: 2150 Mhz
Memory straps 1625
VDDC (Memory/VRM Voltage) at 925mV
TDP (Thermal Design Power) 120Watt
Set fans to keep cards at temperature of 70°C

Remove all the software you used before (like wattool), clean all your video drivers using DDU (Display Driver Uninstaller, link: http://www.wagnardsoft.com/content/display-driver-uninstaller-ddu-v17065-released), then Flash your BIOS, Reboot, re-install your video drivers, and test if it works for you.

Credit goes to doktor83 (https://bitcointalk.org/index.php?topic=1843147.msg18619806#msg18619806), and insider00.  

first try this memory strap, copy it to 2000 and 1875 section, be prepared for recovery if the card fails POST.

400D0302777000000000000022AA1C00B56A6D46C0551017BE8E060C006AE6000C081420EA8900A B030000001B162C31C0313F17