[jeffbee]

Yeah, oversized power supplies are also responsible for high idle power. "Gold" etc ratings are for their efficiency at 50%-100% rated power, not how well they scale down to zero, unfortunately. I have never owned a real GPU, I use the IGP or a fanless Quadro, so I don't have firsthand experience with how that impacts idle power.

[zokier]

Gold rating is down to 20%, Titanium is to 10% https://en.wikipedia.org/wiki/80_Plus#Efficiency_level_certi...

[ac29]

Platinum is 90% efficient at 20%, but OP is using a 1600W power supply, so that 20% is 320W. Any load below that is going to be less efficient.