Then don't. Buy a Corsair AX850 instead (same internals, lower price).

I don't think loudness @high load is that important, there will be other, possibly louder fans, like those on video cards. IMO silence @low loads is much more relevant, and that includes factors like bearing noise, which can make even low RPM fans clearly audible.

And RPM graphs suggest that Seasonic is the only one inaudible up to, give or take, 450W (possible bearing noise aside, but San Ace are said to be excellent quality fans). Others can be heard, if you are a silence freak.

I'm really surprised that the 12V voltage diffed as much as 4% in your tests of the Seasonic X-850. From other reviews I've read non of them have hit this high figure (ATX allowes for 5% on the 12V). It would be good if you could present your load parameters for your testing together with the results. Makes it easier to compare our testing with other reviews.