Could I get some advice from experienced New Zealand Trampers? To walk a selection of the great tracks (Routeburn, Abel Tasman, Kepler) under an 8kg pack, would Inov8-like trail-runners be adequate, or does the terrain really call for something heavier? Many thanks.

I did the Routburn and Abel Tasmin (the 3-day walk) in Merrell Moab Ventilator Mids. Inov8's should be fine, on the great walks the terrain is generally pretty good.

Think you'll be fine - I had Solomon canvas boots and they were an overkill for the Routeburn.

The Routeburn and Milford tracks are typically 1 - 1.5m wide, smooth and well graded. You might have to take a bit of care in light boots on the way down from the pass on the Milford: on the day I did it the path was getting washed away by the rain! But if you're used to walking on British hill tracks in your Inov8s you should be fine. I did the Abel Tasman in Inov8 330s, and they were perfectly adequate. Away from these honeypot routes, the going can be a lot more variable, though.