High Defense Scenario Gear ChoicesFollow

When in the damage calculation is PDT-% applied? Does it even matter? I wonder because I'm debating on how useful certain pieces of gear will be in extremely high defense situations. For reference the target mob in question is Charybdis, but the information I seek has implications on other mobs as well.

I haven't done the exact math, but my guess is that with pld/blu and pescatora I could get ~800+ defense.

Potentially important factors
1. Shield skill 300+
2. RDM with capped phalanx II also using bio II
3. Simba buckler for more consistent damage

In the given scenario how would the following pieces of gear rank? What would cause individual pieces to move up or down in the rankings?

1. Jelly Ring (-5% PDT)
2. Patronus Ring (-2% PDT)
3. Robust Ring (5 vit)
4. Unyielding Ring (3 vit 7 def)

To build on the above post, PLDs have so much defense that, while technically not being useless, you don't see a huge decrease in damage for focusing on higher defense. Anecdotally (deleted all my parses on accident when removing some things from my computer...), I remember taking 30 less damage per hit than the /WAR using the old Koenig set and defender (I was /NIN and in my TP gear). Give or take 20, and it's really still not a big deal. I'm sure someone else can quantify it far better than I can.

It's also been my understanding (could also be wrong) that PDT is calculated just before the damage is actually applied, i.e., the engine calculates the damage done to you and then applies the PDT just before it sends the message of how much damage you take. -PDT% is VERY worthwhile in this game. The only thing that will occasionally be better than -PDT% is raw damage reduction, i.e., Phalanx (depends on how much damage you take, of course).