[Graham]

You said you were getting some PCS grey tyres, did you test them?  I'd be interested just to know what you thought of them.

I did get some and tried them on the Datsun, Nissan Skyline and Calibre for size. They feel a nice tyre, good shape and quite soft. But I did not glue & true them for any car. But I know they are currently the control tyre for the East Lancs DTM club class so I am sure they will work well on a plastic track.
However really the club is using them to control the cars performance where the owners are running them against each other. In our case there are many different track types so it is better to allow the entrant to decide which tyre is best “overall”, as we see now some slower cars have the bigger advantage  when their tyres work best on some tracks. So it makes for a better contest than if everyone uses the same tyre compound which favours the cars which are just the broadest or best balanced.