The question of what line to use is not a simple one.
Obviously for strong winds or buffeting wind that applies a sudden strain, a stouter line is needed.
If you are flying on dyneema line, you can do that without much weight penalty, but that's the downside of using heavier dacron. There was an interesting experiment (I can't recall if it was in FB or Kiting Mag) where Ken Conrad actually put a strain gage on peoples fly line and it showed that they pulled far less than people thought.
So for the small and medium sized lifters you are considering, what you are risking is the kite breaking free and landing in a tree or in the next state. There are safety concerns with big lifters that make using the recommended line imperative.