you could be right. however an OC'd ant is drawing about 400 watts to have a 500w PSU at 80% of it's limit is no bueno. by crobar, i meant to push it beyond its limits or to failure. my 1300 PSU turned out to be faulty (blown cap). the 600 still works well, just not well with my ant. that has been my experience...YMMV.
It's not a matter of whether I'm right or wrong. I was merely stating facts together with sound numbers to back it up.
An 80% load is still acceptable and seems to be the consensus threshold of maximum load especially for a 24/7 operation. However, I'm curious about how you equated 400WAC draw at the wall to represent an 80% load on a 500WDC PSU with an efficiency of 85%. Perhaps, you're confusing AC wattage (at the wall) with DC wattage of the PSU and vice versa and not figuring in the efficiency factor on top of that.