given fast.com is served from a local CDN in NZ that doesnt really say much
Huh? I don't understand that comment. does that not mean that would give a relatively accurate test of the download speed being provided by the ISP.
International tests are dependent on international bandwidth and other variables.
it gives you an idea of how well they connect to NZ content, not international. but even if you start having issues to local stuff when where does the buck stop?
these people are having congestion issues to local and internation sites and speedtests, yes they can max out there line to a dedicated vodafone speed test mirror but thats because it doesnt leave vodafones network. it shows there is/are issues in vodafones links to the rest of NZ and international.
the vodafone speedtest server is within vodafones network, where they have complete control over where the data goes and how fast it can get there. if you test to any other server it introduces other variable, like the speed of handovers etc so yes they can "shape" it as you put it to some extent.
If I test to ACS data and/or two degrees Christchurch (I'm in Wellington) then I still get good results. The latency to Chch is higher as expected.
just because you get good results doesnt mean there isnt an issue with vodafones network, i would have they have multiple core networks in wellington and you just happen to be on one that doesnt have any issues. count yourself lucky at this stage.