Need help settling this debate

So me and a friend at work were talking about psu's (as one does at work) and the debate came up about peak efficiency's under different loads. He's saying that a typical psu will operate at peak efficiency at about 50% load. 800w psu @ a load of 400w =max efficiency. Where I'm saying that a typical psu will operate at max efficiency at about 80-95% load. Please any help on settling this matter is appreciated. If you can please link any data on the matter. Also, would there be a difference between modern and older psu's on average.

Need help settling this debate