In wattman, set State 7 for the program as both minimum and maximum, like this. Just click on "State 7" and select "set minimum".
My 480 will reduce clock speed on GPU and VRAM, sometimes causing a crash if I don't do this for both GPU State 7 and Memory state 1 in games where I try to eke out maximum framerates. Set your power limit to +50, it will only pull what it needs to maintain State 7. In my case, I'm close to the 180W power limit after doing this with my GPU. (GPU-Z states my GPU is in the bottom 21% of Ellesmere XT chips for ASIC score, it's not efficient at all).
edit: After looking at your power supply, try swapping to the other 8-pin GPU connector from your PSU. Those fans aren't pulling much from the PSU, don't worry about them.