Armor penetration cap?

[Andomar]

I've read somewhere that the cap for armor penetration is at 50%. I have mace spec (15%) and battle stance (10%).

Does that mean I'm capped if my gear gives me 25% extra armor penetration?

[Magnuss]

No, this information is taking into account the affect of a proc from either a Grim Toll or a Mjolinar Runestone which give a substantial amount of ArP from their proc. If you do not have one of these two trinkets then you will have to achieve 75% ArP from gear in order to be at the cap (which is not realistic).

[Andomar]

Wowwiki says:

ArP experiences diminishing returns for target armor lower than 8,317 armor or more than 50% personal armor penetration.

And here's a post by Ghostcrawler

Kinda hard to make sense of it all. Do you know if ArP is good against clothies or against plate?

[Destruyen]

in pvp arp is great against plate, while cloth its better to have strength. in pve however, its good to have as much arp as possible. if you have an arp proc trinket (grim toll/runstone) its good to have around 60-70% since you wont see a 100% uptime on your trinket. the "diminishing returns" of arp past 50% with an arp trinket just means that you will have some wasted arp from gear/gems while your trinket is procced.