I was hoping that anyone with info about any of the tracks down Invercargill way may be be able to add any useful comments or links.
Whilst down south a little while back I took some photo's of track signs etc but haven't completed any of them personally.
As fas as I can ascertain - there are two main options from a MTB point of view:
1) Sandy Point (top left photo)
2) Bluff - apparently there has been a lot of money spent developing the Bluff MTB track