I thought I'd do a quick thread update.
Ended up buying a set of slightly used 235 35 19'' Conti 3s off another forum last weekend, got them fitted and a couple of wheels refurbished at the same time during the week.
So thanks for all the advice, much appreciated and I learned all about Porsche tyre specs to boot! Ta
Watch out for a set of 225 35 19 FK452s hitting the for sale section soon (or maybe I'll just ebay them? Never sold tyres on their own before so don't have a clue about couriers for them - time for another thread on that subject?)