Yes, I agree with Banjo The only puncture that I have had with Duranos on my winter/wet weather bike, about 3000k this year, was because of rimtape failure . I have not had any punctures on the summer bike with Vittoria Rubino Graphene tyres - about 4500k this year. I am fairly well convinced that you have to payup for quality and then not try to run the tyres until the last k of usable life.
Turning to my original qn: from the above comments, I conclude that p******* vulnerability does not significantly increase with lower pressures and that I may as well enjoy the increased comfort.
I have also learnt about tyre drop, a concept totally unknown to me until I read Ajax Bay's post, and the notion of differential pressures between FW and RW. The fgures sugggested by the chart for my 80kg weight say 95k all up load on 28mm tyres on the winter bike are 5.0 bar on the FW and 6.2 bar RW - these seem v low. So, lower I will go but step by step .
Thanks everyone - very instructive.