Armor Penetration question

[Jeckyl1234]

I know that 1400 armor pen is the hard cap, meaning that you have 100% armor penetration.
Does that mean that you ignore ALL of your opponent's armor, thus dealing (true) damage to him?
Me and my friend, playing a feral druid decided to test something and I don't quite understand the results.
I consistently hit him for 2k with backstab in bear form for over 30+ hits, and after switching to cat form the dmg went to 4.5k+ after 30+ hits.
I don't understand how that's possible when I have 1406 armor penetration rating, and what I also do not understand is how I did considerably more dmg with expose armor - which reduces armor by 20%, wierd considering I already had 100%?
P.S. I'm also wondering is it worth going for 100% as Sub for PvP or 91% with Serrated Blades talent ?

[DarkenedHue]

Doesn't quite work like that. There is another Mechanic at play called the Armor cap here, that was created so Arp wouldn't end up too outrageously powerful on high armor targets. There armor cap is a value calculated based on the target's level and current amount of armor. After it's been determined, your Arp % gets applied to either the Armor cap, or the targets actual armor, whichever is lower. That's how the amount of armor deducted is determined. Expose Armor yields a gain on high armor targets because the additional armor reduced is helpful since you aren't ignoring all of it.

The only situations where your arp would cause you to ignore the entirety of the targets armor would be when it's armor value is lower than it's armor cap value, which is something that happens only at very Low levels of Armour.

[Jeckyl1234]

Okay that makes sense, and regarding the rogue talent Serrated Blade giving 9% armor pen, would it be more beneficial if I'm aiming specifically for maximum damage output to get 140 more rating trough gems or get an additional 300 attack power? Does the talent work like I think it does, making it 91+9= 100% armor pen, or does it work like sunder armor or expose armor, making the 140 armor pen rating more beneficial, if aiming for max dmg?

[DarkenedHue]

Assuming that talent works properly (it probably does), you would only need 91% Arp from your gear to reach what's effectively the arp cap. Any arp past this would be pointless and you'd be best off getting some other stat.