We just changed my wife's car from a wild turbo charged Toyota Caldina to a more sedate, non-turbo charged 3.0R Subaru Outback and the premium went up by $150 per year.
The premiums here don't seem to make sense. The performance of the car doesn't seem to have as much weighting as to how many are stolen or crashed.
I have also just changed my Jag and nearly bought another XJR (400bhp Supercharged model) but instead have settled for a non-supercharged model of the same shape (still 4.2L but 'only' 300bhp). I got an insurance quote for both and the premium was $80 less for the XJR! I can only assume that because they are very rare, few have been stolen or crashed so aren't seen as such a high risk.