I'm just going to offer unsupported through actual game play advice that's still actually useful.
To cast word of death without fail, you need 120 skill points. This isn't very useful in PvP.
To cast wildfire without fail, you need 106 skill points. This has some functionality in groups, but I'm not sure exactly how functional it is.
To cast essence of wind without fail, you need 92 skill points. This is one of the only spells that I've actually used successfully in PvP. I plan on doing some experiments with EoW soon to evaluate how I would use it best.
Those are the upper level spells. Some of the more useful spells need no skill to cast, and at 50 weaving, you can cast gift of renewal, attunement, thunderstorm and nature's fury without fail. Renewal, Attunement and T-storm are extremely useful in nearly every situation. But the problem with some of these levels is that it's hard to find a focus group. It's easy at 0, everyone has no skill in weaving. It's fairly easy at 100-120 since that's what everyone wants or needs. But if you only want 50 skill for reliability in the protection/healing spells, then you'll have trouble finding people to make a focus with unless you already know people who are going for the same thing.
Now, my actual PvP experience consists of defending out of the way champs against unwanted participants, so take what I just wrote with a grain of salt. At least the skill levels for 100% casting are accurate.
