You should always use autotuning. The S9s are getting old, i suggest you use a conservative value of 1280 or less.You can also try to match the original factory speed if you want. In any case, the machines probably need maintenance and perhaps repair. Many many many people run them non stop. but at the very least do scheduled cleaning.
Using Braiins OS+ with autotuning enabled does in fact extend the lifetime. If problems develop, the tuner will catch it and readjust as needed, with manual tuning the problem would remain unattended until the chip fails. If you want to focus in longevity, naturally lower values are best.
The best efficiency value was achieved at power limit 900W with target temperature 60° by Bas Laurier (70 J/TH). S9s running like that should essentially last until the parts break from being old which is normal for them anyway.
Okay thanks for your reply.
Right now most of them use the default 1420W as max. I will try and reduce it as you suggested. Cleaning is part of my schedule - the place is quite clean though. Repair is very difficult because I did not find reliable people for that here in Europe.
Do you know anything about the Bonus-Problem?
I usually get about 0,3-0,4 % Bonus instead of 2 %