if there is space around the components it dosent take too much to keep a PS cool.
(On my Crossflow I shut down the fan to see what would happen it ran 6hrs and just was warm)
But if its tightly packed the heat transfers to other parts making them warm as well.
The 80mm fan on the Silverstone can run quiet at normal loads but when the load raises so does the speed/noise....
25 dBA @300W or below, 30dBA@ 550W, 42dBA@ 1000W