Very good. But my reasoning wasn't reliability, it was efficiency. The curves on most if not all PSUs go all to shit when running under 25% or over 80%.
There isn't much difference for anything 80-Plus rated. For example Seasonic 1250W unit.
I hope I don't sound like a SeaSonic sale rep but here is my favorite mining rig PSU:
http://www.plugloadsolutions.com/psu_reports/SEA%20SONIC_SS-1250XM_ECOS%202811_1250W_Report.pdf100% load - 88.7% efficiency
80% load - 89.8% efficiency
50% load - 91.4% efficiency
20% load - 89.8% efficiency
Also look at the "curve" it is almost a flat line compared to the bell curve shaped efficiency curves of a decade ago. 80-Plus may be imperfect and sometimes a lot of marketing but it has widened the "sweet spot" of PSU load curves.
IF SeaSonic says it is good for 1250W @ 120F well I am going to find out.
If it can't do that they shouldn't say it. Given they have 5 year warranty they have a lot more to lose than me by over promising.
That being said loading to 80% isn't "bad". It gives you a little headroom as the PSU ages. It is a lot better than the "50% rule" nonsense which was common around here even just a year ago.