In reply to neilwiltshire:
welcome to the kiwi way. That is a small pack by traditional NZ standards! But good enough these days with all the small kit. They are talking about something like a Macpac Pursuit, or if you like a bit more gear, an Ascent. I pretty much use a Pursuit for most trips like that (comfortably), but can compress to much smaller (25l) when need to for one night warm summer conditions stuff. Although I would not do that up the Tasman or Aspiring regions.
Unfortunately, you need lots of space for rain gear!
But that Deuter Guide would do the trick. You will just need good quality light gear such as sleeping bag, shell gear, bivvy bags or whatever. The numbers are all over the show for pack sizes.