I have run more flights and tests now, and again must change the theory.
REX2 meanwhile was reinstalled.
Temperature in my case has little to do with it, I run the tower closed again, and there are no changes in temperatures.
I then tested the ingame sliders, and here is where the dog is buried (German proverb...
). It is the traffic sliders. That the car traffic on world roads puts a lot of stress on the CPU, was known since long and I had completely deactivated it anyway. But what really makes the difference between freezing system and non-freezing system is the ordinary air traffic. I know that some people run these sliders at settings between 10 and 25% for the most, and have no problems with the PNG737. But for me, it does not work, even when my system compares to theirs. Putting all sliders to 0%, no traffic whatever, has given me a dozen flights by now with no freezes anymore. I have clouds maxed out, and maximum vieiwing range, all nice. I have special airports sceneries which come with their own APRON traffic schemes, all nice. I use REX2 with live updates, all nice. Add air traffic - and the flight freezes after some time.
Well, the world may be a bit lifeless now, but at FL270 it always is a bit lifeless anyway, so I can live with it.
My beloved 737NGX is back in regular service!
Fantastic package.
The only thing that remains unexplained is why all of a sudden, with no installation changes, the AI traffic messed up the sim, and remains to do so even after reinstalling everything. That'S what I would like to know. There were no hardware changes on my rig since I bought it 16 months ago. Graphic driuvers occaisonaly were chnaged, but always going back to 275.33, since all later drivers up to the recent 301.xx were unstable.