Update on the PMS exhaust system (to help those who search for a PMS exhaust thread).
I attended a Brand Hatch track day, got 91 DB on the static and no issues on the drive by - limit was 87 DB.
I have also attended a Goodwood track day, got 85 DB on the static (I think I rev'd it a little lower than Brands) and had no issues on the strict drive by - limit was 92 DB, despite the exhaust system back popping. I have to say this exhaust system adds to the race car feel but helps having no rear interior.