Tom,
What sort of Pirelli's did you have on the Porsche?, and how old were they?.
I have experienced tires before that have gone off, due to their age, and thus the compound is no longer as soft as original when made. This is why you should store tires in the shade, i.e. out of direct sunlight.
While this message is not supposed to be a Pirelli advertisement, Pirelli like all manufacturers make a range of tires, some for the family car (where the first priority is safety and long lasting) and some for the track or performance driving. I am sure that a P Zero tyre (as fitted to the F40 ?) would be sticky enough
.Alot of Ferrari's were fitted with Michelin's in the 60's and 70's I think so nobody should get upset here.
The one reputation I would say about Pirelli's is that they apparently let go very suddenly when the limit is found .... I have spun violently spun my Alfa on new Pirelli's, but I think that was really my over optimistic attempt at a tricky corner ...
Pete