Dan: that is the right adjustable screw. In the Brewtus III it is not of white plastic anymore. Adjusting it CCW brings the pressure down. Thanks for the tips!
I have read through most of the FAQ posts on the vibration pump and OPV discussion and also noticed the diagram you posted of the machine and where to look for. However, it is still not clear to me what effect different coffee amounts (ristretto, espresso, doubles) would have on the pressure setting. If I use a naked portafilter, the pressure dail now shoots up to approx. 9.5 bar. If I make an espresso, the pressure goes to about the same 9.5 bar. If I use the manometer portafilter (as with a naked portafilter) I get on the dail of the Brewtus III 9.5 and on the manometer 9.0 bar (a little lower). That seems OK. Nothing here is calibrated, but indicative I believe.
Now why would they set the OPV at 11 bar at the factory? If a blind filter delivers about the same pressure as a single espresso, then I would believe a double espresso would be also at the same bar pressure?
Now when I make my espresso I get way more flavor. I was testing some espresso blend of Miscela d'Oro from Sicily. At first (with the higher pressure of more than 11 bar) it tasted dull, but now it is way better.
So, I am most likely

not understanding why having the right OPV setting will not make much of a difference.
Thanks for all the help. It is here now almost half past 2 at night and my wife probably thinks I am completely mad with this coffee stuff staying up that late.
I read somewhere else that you might be updating the review of the Brewtus II to include Brewtus III info. If I can be of any help, let me know.
Sjoerd Jan