Which Tyres?

So much for Conti GP4 Seasons.

They cut up like shit, was alarmed to see how many cut it got when a customer came back with a puncture after a couple weeks.

Perhaps I need to reduce the tyre pressures? What is the optimum psi for a 23c in winter?

25c, if you're 65kg, you can easily drop the rear to 80psi and front to 70psi (or less), no point in going for 23mm at all, unless you want to run mudguard.