Has anyone experienced problems running 650 mhz and up on the standard bitmain provided awp3 psu? The 1370 watt drawn at 650 mhz seems disturbingly close to the 1600w max on the psu since 1600 x 0,8 = 1280.
Typically, this is not the meaning of PSU power limit.
You can run 1300W PSU like EVGA with on-the wall reading of up to 1430W just fine.
i am not sure why you are multiplying 1600 by 0.8.
First, only the worst PSUs have 80% efficiency (maybe APw3 is one of them, i don't know), which is a Bronze level.
Second, PSU indication of 1300w (EVGA) or 1600 (APW3) usually means power output limit (to miner) and not power input (measured at the wall) AFAIK.
That said, maybe Bitmain got it backwards, who knows.
The 0.8 comes from the so called 80% rule. It states that while electrical wirering in general and psu's in particular are able to perform at a 100% at peak intervals, running it long term is not safe above 80% or perhaps with good quality components at 85%. While a few might have good experiences running at a 100% for a long while, the 80% rule is more or less generally accepted.
EDIT: Just to clarify, the 80% has nothing to do with efficiency.