There is also Sifters Brevet, I cant even pronounce it myself !http://sifter-writes-bikes.blogspot.co.nz/2011/02/te-tawhio-o-whanganui.html
Its in Maori. Oh I see, Tawhio means "to circle". The circling of Whanganui sounds about right : )
And, I just found someone else's report on it. http://nzbybike.com/about-nzbybike/the-ride-blog/
I haven't done this one myself. Apparently you can choose your own course, as long as you meet up each night at the same place. I think that's the idea, and because there is accommodation, you don't need so much gear.