That Kiwi SR looks tough. Lots of decent hills and Arthurs Pass right at the end. It sure ain't the topography of Essex.
I knew why there was a reason I am a kiwi in London - I do these long rides in East Anglia and all my Kiwi Mates think they are EPIC and AWESOME because in their heads they are thinking of their topography, which is kinda 'hilly'
Also factor in the that there will be not many people doing it, so not much in the way of bunches. At least it's in the south Island so riding on main roads won't get you killed like it does in the north.
Am I selling it to you? Actually it would be an AWESOME ride and your jaw would be on the ground from the scenery and sense of being in it