Faster Casting vs. Penetration

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PaperRat wrote:

Doesn't penetration affect reflected damage as well?

No, reflected damage carries no special properties and cannot trigger any effects that require a hit because it doesn't count as one.

Pen just doesnt change tooltip dps, which is the main reason I guess

I usually use this rule of thumb:

> 2/3 damage of a single element and cast speed > 2.0 casts/sec without faster casting => penetration all the way!

< 1/2 half damage of a single element and cast speed < 1.5 casts/sec without faster casting => faster casting.

Everything in between depends on the specific skill or intention of the build. It is always a bit of a tradeoff between what is most effective and what gives you good feedback and enjoyable gameplay.

Math illiteracy ahoy.

FC is a more multiplier to dps but one that you scale linearly. (Outside of Spell Echo anyway.)

Think of a simple equation like this:
DPS = (base damage) * (1 + damage increases) * (more multplier 1) * (more multiplier 2) . . . * (1 + cast speed increase)

Penetration would exist in one term and cast speed in another.

A perfect quality FC is roughly 50% cast speed by itself, which is effectively a 50% "more" to your dps even before you multiply it and your cast speed base with Echo. (Where the "1" in the above equations represent whatever your base happens to be normalized to "1" for the sake of simplicity.)

Comparatively, penetration is around 35% more to a single term in that equation. But that's where things get tricky. because effective hp increases geometrically at higher resistance totals than lower ones. The 5% resistance going from 75 to 80 is not equal to the 5% going from 70 to 75. Stripping even a little resistance off the top makes a huge difference to your effective dps.

The resistant mobs act as speed bumps and Penetration makes it easier to climb them. And it's likely you didn't need help killing the trash anyway. A mob that has 75% resistance is four times more resilient to your dps than one that's at 0%. Dropping that resistance to 40% makes it only a little more than 1.6 times more resilient.

Put in simple terms, think of resistance as a "more" multiplier to defenses. Getting rid of the "more" to defense is powerful for that reason.

So it boils down to what you want to achieve. I've seen Arc used merely for clearing trash without Penetration. The whole Arc+Empower+FC+Echo Foxtactics combination is fine for that, particularly if you have some other single-target skill that you use.

FC is also just plain better for checking for crits. The faster you throw the dice, the more likely you're going to get a crit. It averages out the RNG of crit. As the number of rolls approach infinity, the more averaged out your damage becomes.