I don't go into a lot of detail, but on Watermelon's web site is a little description of our trip from the Solomon Islands to Fiji. It's the Christmas 1995 log, http://www.cruiser.co.za/hostmelon34.asp
I think that New Caledonia is too far north to give you a good angle on heading east to Tonga or Fiji. Many Kiwis make New Caledonia their last stop westward before heading home for cyclone season, and then sail north again the following season up to either Tonga or Fiji, where they have more of a reach than a beat to contend with.
Too close on the wind and you will find yourself making little headway in the winter trade winds. Better to make a big sweep either south or north to get a better angle. Not easy, but possible.