Just thought I'd add something - I just fixed my IPv6 tonight (forgot to save my switch VLAN configuration and had a power cut recently) and have been testing this via my IPv6 testing SSID, on wireless to my Chromebook along with my standard network SSID which currently has IPv6 disabled.
IPv6:
IPv4:
This is not at all scientific - heck I am testing this over WiFi on a Core M3 powered Chromebook but interesting that upload is not really affected.
Also, from what I have heard from people who work for 2degrees in their broadband and datacentre side it is still pretty-much Snap internally, and still based in Christchurch.
Also pinging @NickMack who may know something.