With the new system of elemental damage, I was wondering when given the choice (for a reroll at the Mystic) if I should pick elemental damage over another historical damage stats (like Crit Chance or Crit Damage) ? How does elemental damage affect my overall DPS compared to those stats ?
Since the 2.0.1 update came out, elemental damage has been the bread and butter of every class. Every skill in the game was given an elemental type (Fire, Poison, Holy, Physical etc.) in order to allow player to benefit from the new items affixes +X% to element damage
Let's take a quick example :
You are playing Wizard with the skill Ray of Frost. As you can see, the skill deals 510% weapon damage. Let's assume you have a legendary bracer that add 20% damage to cold skills, Ray of Frost now deals 510% x 1.2 = 612%.
Now imagine you have a Stone of Jordan equipped aswell giving you another source of 15% cold skill damage. Since elemental damage is additive your total bonus to cold skills is simply the sum of all your bonuses. It will be calculated as follow :
Total bonus = 1+ 0.2 (bracer) + 0.15 (Stone of Jordan) = 1.35. Ray of Frost will now deal 510% x 1.35 = 688,5% weapon damage.
As you can see, stacking %elemental damage is immensely powerfull and provide a more stable DPS than Crit Hit Chance (CHC). The CHC and Crit Hit Damage (CHD) are complementary and rely on each other to be efficient (you need a good balance between both in order to output a good DPS). A normal character will usually get about 9.23% total damage increase from the 6% Critical Hit Chance stat (because it depends on the CHD number and the attack speed for more or less Crit Hit). If, instead of that stat, you went with 15% element damage you would be getting a huge 15% total damage increase to all your element skills.
What the 2.0.1 has brought with this stat is sustained damage. You don't have to rely much on the 50% CHC and 400% CHD to deals big damage but instead your damage are better constantly. Of course a well end geared Character will benefit from both elemental damange and the couple CHC/CHD. But at low level or when your gear is not finished, I would advise to go for elemental damage when given the choice.
Here is a good summary on how +Elemental Damage works:
The video advises a good way to estimate if a new piece of gear with +Elemental damage is worth equipping: If you have one piece of gear with +20% fire damage then your damage looks like this:
100 * 1.2 = 120
120 / 100 = 1.2 = 20% Gained
If you are looking at adding another new piece of gear with +20% you can calculate the damage gained by:
100 * 1.4 (+20% on two items) = 140
140 / 120 = 1.166 = 16.6%
Which means adding a second piece of gear that adds +20% fire damage only nets you roughly 16% damage. He goes into much more detail in the video, but this is a nice way to determine if that item you found is worth it.
You should prefer Elemental Damage over other stats in the most cases, meaning you want to keep a good balance between Elemental DMG and other stats.
Let's assume you deal 1000 DPS, have 20% crit chance and 200% crit dmg and 0% Elemental Damage.
You will result in 1000 + 2/10 x (1000 x 2) DPS = 1400 DPS
If you now add 20% Elemental DMG (that's the maximum an amulet can provide) you would result in 1400 x 1.2 = 1680 DPS
If you would instead add 10% crit chance you would be at 1000 + 3/10 x (1000 x 2) DPS = 1600 DPS
So with this assumption you would end up in a DPS loss if you would go for the crit chance. This is the because because we are assuming we have a default 0 Elemental Damage.
If we now look at the same calculation having 1000 DPS, 20% crit chance, 200% crit dmg BUT 100% Elemental DMG already it looks like this:
We are dealing right now (1000 + 2/10 x (1000 x 2) x 2 = 2800 DPS Now we get an item which upgrades our Elemental Damage by another 20%, so we have (1000 + 2/10 x (1000 x 2)) x 2.2 = 3080 DPS
If we would reroll the 20% Elemental DMG into 10% crit chance we end up with this: (1000 + 3/10 x (1000 x 2)) x 2 = 3200 DPS
As you can see the crit is way better after you got a decent amount of Elemental Damage, same with +Elite DMG, crit hit dmg, strength and attack speed.
What does this mean?
You should always have a proper balance between ALL stats, and not only the commonly known 0.1% crit chance for 1% crit hit damage. Try to balance, having for example 5 items with crit chance, 5 with hit damage, 5 with elemental damage, 2-3 with elite dmg and a few with +Skill DMG% (your mainly used skill preferably)!
Additionally Moldran calculated around this a bit too and i link you the video he made: