Aye, others cars I've had with catback sytems are louder the higher the revs, but they were NA, not turbo charged, it is odd though. I'll have to get someone to drive by, or record a drive-by at full chat.
This is with the symposer unplugged, I'll have to get a blanking cap as its far too boomy and odd with the exhaust and symposer. with the symposer on it's less noticeable that it is quiter at higher rpm. I'll have to find a sports cat for sale second hand or buy a new decat, I can't be arsed paying over £400 for a sports cat. I think I'll follow your avice and once it does go for a map, do a rolling road session before and after.