Entirely with Rambaldi here, obviously someone who knows the place.
Also have to disagree with a few other North Island statements above.
I reckon it's the best choice for a single week of NZ travels...and would highly recommend to rather "do" one area a little more in depth than trying to string together 500k' days.
Easy enough on the dopey straights in Oz, but entirely non-applicable in NZ.
North or South.
I'd suggest to spend that week NOT through the center of the NI (which means LOTS of bike time, lots of k's but little time for anything else) but the Northland (everything north of Auckland) and maybe add the Coromandel (and not just the loop!), if there's enough time left. Work with a 250-300k daily average if you actually want to see something of the place, get off the bike to walk up a lookout or a rock-arch down the beach, a scenic lunch on a beach with locally smoked Hoki etc.
A million bends, never-ending hills, lots of attractions of all sorts and never more than 50k's away from a magnificent coastline, fabulous beaches, National Parks, Forests etc.
Better weather, more stable than the SI (west coast in particular) and by far not as overrun and plasticky/ touristy as many of the SI hubs.
Here's the link on a TWO-week Northland (north of AKL) yarn with LOTS of pics, most places are reachable via sealed roads.
Looks like we might be swapping doorhandles at the the AKL airport then
Will be there with the AusTouring crew for a 2week North Island ride to map the Wairarapa area north-east of Wellington in March/ April.