Well just an update to an old post for those that are interested and still following this thread.
My ladyfinger bananas have been out for a while now (2 winters) and growing very well. No bananas yet.
I also have ABYSSINIAN BANANA, (Ensete Ventricosum) grown from seeds. These do exceptionally well here in the lower north island. They grow extremely fast and are great for that quick tropical look.
Our last winter was not bitterly cold, think there was just one or two days that reached 0. A few light frost days though. All bananas were unaffected.
I have purchased some musa basjoo seeds from Canada, these arrived early Jan. My first one came up yesterday. These are suppose to be one of the most cold tolerant bananas in the world and they can be grown all over the US, and even Canada. Therefore they should not be a problem for most of NZ. I will post an update in a few months to let you know how they are coming along.