Return of Reckoning

1- I've read mitigation from armor cap is 75%. Which is, I think about 4k armor at level 40. Is there a point going over?
Sub question : is overcap armor countering armor penetration? Sub sub question : How much armor pen have average melee dps?

2- I've seen that "lowered chances to get critical hit" and initiative do lower the chance to get critically hit in the character sheet to a minimum of 0%.
As I understand it without this everyone has about 20% to get critically hit, which adds up to the attacker's additional critical chances (am I wrong?).
If one drops his own chances to get critically hit through gear to 0%, will they still be critically hit if their attacker has added critical hit?
Can one drop the chances to be critically hit UNDER 0% to reduce this? If yes, where does this information shows?

3- If I understood well :
Block can avoid any damage. Scales with toughness.
Parry can avoid melee damage. Scales with weapon skill.
Disrupt can avoid spells. Scales with Willpower.
Dodge can avoid ranged attacks. Scales with Initiative.

So for a tank with a shield the value of them would be Block > Parry > Disrupt > Dodge
Which makes sense with the RR point prices of the Renown abilities 1% Block = 3% Parry = 3% Disrupt+Dodge
However the Talisman prices seems to implies that 6% Block = 6% Parry = 6% Disrupt = 6% Dodge. Am I missing something important or are the item pricing a bit whacky?

4- I've read Toughness does not reduce the damage in PvE. Is it true?
Should I put only Wound for PvE?
Is armor of any use in PvE beyond 75% physical damage reduction?

5- Are abilities with tooltips indicating "extra threat" actually doing that?
I've found that on my IB, rolling damage abilities like Heavy Blow do much more aggro than using Grudging Blow.

1. yes there is reason to go over 75% Armour because there is armour debuffs + Armour penetration. Lets say you have 5k Armour and enemy has 25% armour pene, then you will have the max 75% Reduction from armour.

2. You can go Under 0 chance to be crit but this information does not show anywhere. If you have -10% Chance to be crit and attacker has 25% Crit chance will have 15% crit chance.

4. Toughness is basically useless in PVE because the mobs hit so hard that its better to go for super high armour,resistances and avoidances.

Thank you, about 4:
Why super high armor if the cap is 75%? Do mobs have armor penetration? Is there a higher cap in pve?

Mobs have stats and skills, debuffs etc yes=)