50 TO 70 PERCENT LOAD IS OPTIMAL--
The PSU will degrade faster at higher load. That is the fact. A good PSU will work at 90% load, but it will wear out at a faster rate as the components degrade more rapidly. --scryptr
Optimal for what? It's possible to argue that if you won't unpack your PSU it will be even better for its longevity. However personal attachment to the quality of the PSU capacitors and/or whatever internal components may degrade with time should be outweighed by the practical needs and financial reasoning...