I run two huge PAs on my Corvette (efficient), it took some getting used to I'll admit, but I can reliably hit with them now.
-Don't bother firing beyond about 1.2km, the AI will just dodge it (may be different in PvP, I haven't done too much of it).
-Don't bother using them against agile craft (I don't use them against anything smaller than a FDS, unless I see a perfect shot).
-Learn when your opponents are vulnerable, if they're pitch turning consistently, or they're trying to hard-turn (and therefore stalling out for a few seconds), that's the time to line up a shot.
PAs can be rediculously effective, but their balancing mechanic is their travel time. You have to pick your shots to get their full potential, and like said, practice is the best way to learn when/when not to fire. Youtube is also a great way of learning how others use them effectively.