Thanks for taking an interest in my problem.
I started with 416.78 QNF which looked the most recent (and likely to work best with very latest Windows 1809).
But I have since tried other video card, both AMD 5450 and Nvidia GT 720 and none of them work reliably, with hangs and random BSODs a few a day, so I have been trying to trace the cause. A 24 hours memory test passed OK and a CPU stress test runs for an hour at a steady 50 C, suggesting that it is a software rather than a hardware issue.
Running a test video on repeat only lasted an hour before a hang.
I note the the motherboard tool AMD Master does not run at all with the Quadro card, and only for a short time with the other cards.
In all, I am less suspecting video card drivers (though past experience has been that they are always No 1 suspect).
Suggestions stil welcome.