Are you using Overdrive? it seems to be maybe working on keeping the temps below 70 degrees for some reason on the Fallout 4 video with the 480. Try increasing the fan speed and the target temperature in overdrive. It might be AMD's old Powertune. Is there a way to disable Powertune?
If your running Crimson ReLive you can set the target temp, I think the default is 70 or 75. Increase that and the fan speeds and see if that helps.
Check your motherboard's BIOS and make sure the PCIE lane is set to 3.0 speed, it might be on 1 or 2. It should be enough to have it on Auto If your three options are Gen 1, Gen 2, Auto. I think Auto is Gen 3.
Also the NB PCIe configuration in your motherboard Bios set the PCEx16 link speed to Gen 3.
Make sure you have the Power Limit set to the highest + percent (%). It will be either +20 or +50.
Make sure your computer power plan is set to Performance..not Balanced.