I've got a bunch of S9j's and they all seem to run most efficiently at 900 watts. If I'm running all three boards, I typically 3d print a 6" duct adapter and remove the fans an use an AC Infinity inline fan. If I need it silent then I'll run a single board with cardboard stuffers and replace the fans with Arctic P12's.
Discussion
Thanks for sharing! Are you using the AC Infinity S6 or another one? I struggled to justify the cost of the S6 over a standard computer fan. I was curious if anyone had tried the P12s! Opted for the noctua only because of the higher 3000 RPM model though I don’t often run them that high