I'm surprised no one has mentioned Porsche Insurance! Dealt with by Marsh Private Clients who were by far the cheapest for me when I searched about 4 years ago. I search each year and they are always cheapest or can explain why not ("sir, but you do realise they don 't have .... - If you want us to remove it from your policy we will be cheaper")
Full RAC cover included in the price as well - you phone a dedicated Porsche specialist at the RAC and apparently a big note comes up on her screen saying "DO NOT REFUSE ASSISTANCE" when they access my account.
On their website it tells you a contact name as well as the telephone number and that is the person who will answer the phone. They are a thoroughly professional company used to dealing with people with lots of money who expect the best service possible - and they give that same service to cheapskates like me
