So it looks like we'll be doing Christchurch > Clockwise loop up along the west coast and flying out of Wellington. Looking to book flights and it seems marginally cheaper to fly INTO Wellington and OUT of Christchurch.

Any reason to make a definitive decision about whether it's best to "go up" the south island or "travel down"?

It's sort of like.. doing mt cook+milford+queenstown first vs doing them last... Hmmm!