First off I have never played one before, these are just observations from theory-crafting for the build i'm going for.

For my third soul which will have around 5-8 points I'm thinking Sab or Bard.

If i go Sab it would be mainly for ranged finishers and burst (eg throw 5 charges, use the combo then build 5 combos again burn them and then detonate charges) . From what I've seen of the soul tree only one thing makes them OP'd, if how i read it is right, is Charge Booster (+1 to charge stand and 5 different types of charges making it 10 all together), and since I won't be going that high I was wondering if that kind of strat would work well in PvP? (PvE dmg doesn't matter if dots or burst so meh)

Otherwise its the bard for some heals and group friendlyness