Penetration Questions

How much elemental penetration is to much? I don't understand the curve on the wiki. I can get over 100% pen in my build, but it may not be worth it to use the penetration gem and instead use another damage source. What are your thoughts?

It depends on how much penetration you already have, and your goal for the character.

Penetration stacks additively. This means that stacking Penetration too high will have diminishing returns, just like Increased Damage sources.

Here are some examples:

60% penetration vs a 0% resistant enemy will basically give you 60% more dps.
60% penetration vs a 75% resistant enemy will give you 240% more dps.

Adding a penetration support, giving 37% penetration at level 20, will have the following results;
97% penetration vs a 0% resistant enemy will add a total of 97% dps, or 23% more dps compared to 60% penetration.
97% penetration vs a 75% resistant enemy will add a total of 388% dps, or 43% more dps compared to 60% penetration.

You see that penetration is much more effective against highly resistant enemies. Therefore the question you have to ask yourself is "Am I going to be fighting enemies with alot of resistance against my element?" If "Yes" then Penetration is the way to go. If "No" then other supports may be better for you, like Elemental focus which adds 49% more damage at level 20.

In general stacking more than 40% penetration doesnt really help clearspeed much. More than 40% is good vs bosses and rares with resistance buffs.

As with all things in PoE it really depends on your build though.

You can reduce a monster's resistances to below zero with high penetration. The effect from penetration tapers out below that value, but it's still as good as a MORE modifier of the same value.

So if an enemy has 75% fire resistance and you have 100% resistance penetration, the final resistance will be -25%, which means 25% MORE damage than at 0%.

i think i misunderstood the thread title, i was expecting a different kind of question -_-