And yes, it can go 120MPH. Take it to a race track and how many laps will it go till something gives? Now back at 60, how long till something fails?
Same idea here. If you want reliable systems you tap the PSU for about 50% of it's max rating.
Another reason is that some PSUs when they fail, do so catastrophically. http://www.tomshardware.com/forum/304723-28-system-components is one of 100's of posts about this.
My designs run 50 to70% of max. And if I have the time I hook up a P3 Watt meter and want to see under 50% of the PSU rating.
I want to do a new build soon with 2 Opteron 6272's, a supermicro H8DG6-F, a few fans along with 2 HDD's and one SSD. The extreme PSU calculator says around 738W peak usage (so 100%) and 690W at about 90%. In light of all of this, would I be able to get away with this 750W PSU: http://mypccase.com/sppor75at23s.html
Would that be cutting it too close? I'm open to suggestions.