Wow I've always wanted to see New Zeland, this just gives me yet another reason
I like running the lightest sway on just about all tracks unless really bumpy. I like having the tighter feel more than the soft & forgiving feel.
You may want to try tightening your diff as well. When you spin out does it look like just the outside wheel kicking up dust or both?
The way I tune my ball diff and slipper now is like this and it's been working well for me.
1. Find the toughest turn in regards to keeping traction on exit.
2. Start with loose diff tight slipper
3. Come out of the turn and hit full throttle to make it spin out
4. Tighten the ball diff till either both wheels spin out or I get too much push around the rest of the track
5. Then loosen the slipper until I can't make the short run-up jumps/sections
6. Adjust punch on esc, or expo on Tx, or travel limit on throttle, or just lay off the gas coming out of the turn to prevent spinning out.
7. Make the best measurements I can on the slipper nut distance from the end of the shaft and the amount of turn put on the diff so I have a good starting point next time I come back to the track.