Dont stress too much about the width (As long as it is more like the 3+ lanes wide like Antrodemus says) as long as there is adequate run off areas provided wherever possible. The V8's handle Surfers Paradise OK and the Clipsal 500 at Adelaide is still hailed as one of their best events despite that being on public streets....
The most important factor will be to provide numerous 'good' access/facilites for officials to clear damaged cars &debris away quickly. There is nothing more boring than watching a street race run behind a safety car - Its probably this fact that killed Canberra....
Roll on Wellington - Shhhh, some Aucklanders may be reading this
