I've been testing a lot lately with different wattman settings and so far, this is the best I can get. My main goal was to lower the power use as most as I can without impacting the hashrate too much and also lowering the heat and noise. So I just want to share what I have been using now to help others.
I have 6x XFX 480 4gb models. At first, I flashed them all to 8gb, but I flashed them all back to 4gb, due to the 4gb having 1750 memory clock instead of 2000 memory clock, which will lower power usage without impacting hashrate that much (probably due to better memory timing straps).

I just change state 7 to 900, voltage for gpu and memory to 800, power limit -30%, and change the fan speed and target temperature to my liking's.

Here is my GPU-Z showing my settings stuck even after flashing from a 4gb to 8gb and back to 4gb.

Here is me running Claymore 4.7 with ETH mining only and showing a stable hashrate of almost 24 mhs per card with GPU-Z graph.

Here is my whole rig power usage with 6x RX 480.
So far, I'm pretty happy with the results with the whole rig only needing about 670 watts at the wall.
If anyone else can figure out a way to lower power usage even further and still stay close to 24 mhs per card, please share. Thanks.
Anyways back on toppic i have a rx 480 rig all 8gb , everytime i change the settings in wattman i notice they revert back
and sometimes crash even, another thing i found is turning the power limits below neg 15 reduced my hashrate by alot so i cant do that.