I have my CS and MB 560 SEC insured with American Collectors Insurance. I've had at least one car insured by them for over 10 years. Early in my relationship with them, they also offered track insurance for cars being driven in high performance events (like Drivers Ed that BMW, Porsche, etc. sponsor). I had my '87 Porsche 928 S4 insured with them, and was driving it about 15 track days a year.
In the 3rd year of insurance, I had a 'hard impact' at Mt. Tremblant that totaled the car. There were minor delays and complications since the car was not drivable and located in Canada. But - within 10 days, everything was settled, they made fair value payment for the totaled car and I bought it back to salvage for parts at about 15% of that value.
I felt their service and their settlement were both excellent, considering the circumstances. Thus, I'm still their customer 10+ years later (they no longer sell track insurance, however!!).