Post by furrymammoth
I asked here before and also asked wow.com's the queue. Because most raids will have faerie fire and sunder armors, getting rid of at least 30% of the armor anyway, that makes each point in ArP 30% less effective right off the bat.. My OPINION is that it isn't worth speccing into, at least for hunters. There's a lot of "ifs" there- "If you can stand still, and if you are MM, and if you only use aimed shot, steady shot, and chimera shot, and if you have 500+ ArP, and if you have an armor pen. trinket, only then is it worth it."
I don't think its worth it. A hunter's mobility is one of its greatest assets, in my mind. taking away arcane shot takes away some of that mobility, that's another 33% of steady shots (ish) that you need to stand still for. wow.com
Armor penetration: Does the %reduction apply to the amount of armor my enemy has before or after the sunders are applied? For example, if some mob has 10000 armor and has been sundered 5 times, i would (before ArP) be attacking against 7500 armor. If I had 15% reduction, would it reduce the effective armor by 1500 or by 1125?
The % reduction applies to the armor your enemy has after armor-reduction abilities are used. Taking the example of a mob with 10,000 armor here, you are indeed attacking a mob with 7,500 armor assuming that 5 stacks of Sunder Armor and Faerie Fire are both up (these effects are additive). To my knowledge, Blizzard hasn't released exact details on boss armor, but most theorycrafting sites agree that the average Wrath-era boss is rocking 13,083 armor. If your raid has FF and 5 Sunders up, your Armor Penetration should thus be calculated on a boss with 9,812 armor (or 25% reduction).
With that said, you are never going to get as much effectiveness from your own Armor Penetration as you see on the tooltip. The math here gets a little more complicated, but Less QQ, More Pew Pew has a great post here on the post-3.1 world of armor penetration and how to figure out exactly how much benefit you'll get from your own rating.
Post by Argg0
Reaching the 100% cap is only possible (with the current gear) during trinket procs.
Arcane shot gets beaten by Steady Shot by 200ish, 300ish ArP, without trinket (remember, you are also respecing out of Imp ArS and specing into something else).
If you wanna be sure, use the spreadsheet or www.femaledwarf.com
(though, I think the spreadsheet is a lot easier to use and do quick comparisons).