If the power supply says it is rated for continuous 850 watt, it is good for 850 watt DC electricity 24/7/365, otherwise it wouldn't be called "continuous".
An 850W 80plus GOLD power supply is 100% spec when you are drawing approximately 965 watts at the wall. You are fine. For what its worth, I drew 910 watts AC from a NZXT HALE90 750 watt, approx 8% over spec. It didn't break a sweat.
er no.........
3R system as an example..... GOLD rating , but the internal components are only designed for <50% of the product STATED full load capacity.
Some manufacturers overrate the components, others are just bottom feeding scum that use industry terms to scam people.
Also 'Continuous' is a relative term and depends on the background ambient....