QUOTE(jenga201 @ Oct 21 2016, 16:26)

I have questions for somebody that understands proficiency calcs.
What would be the real benefit of having 600 Prof vs 700 Prof?
Would it translate to just a couple % of counter-resist?
What would be the real benefit of having capped Prof (1000)?
Would the counter-resist actually be worth the lack of magic score?
These questions apply to both Holy and Elemental separately.
(Excluding counter resist from Staffs)
Including Staffs, from what i've experienced;
Using Katalox or Redwood allows for use of Prof gear. Meaning 3 Phase 2 Prof is about the same damage as 5 Phase.
Using Willow or Oak does not allow for use of Prof gear. Meaning using any Prof is weaker than using 5 Phase.
Does this mean that the counter-resist gained from Staffs is roughly equivalent to capped Prof?
QUOTE(Superlatanium @ Oct 21 2016, 20:25)

Big. Holy/dark is great for no-Imperil style, elemental is bad for no-Imperil style. Holy/dark is OK with Imperil style, elemental is good with Imperil style.
The main benefit of proficiency is not the additional counter-resist (although that's a bit helpful), but the increased mitigation reduction.
High mitigation reduction is essential for Holy/Dark using no-Imperil style, for obvious reasons - without Imperil, you want to reduce mitigation as much as possible, else monsters will be pretty resistant to your element. I think this means 3 phase + 2 proficiency in most cases.
Holy/dark with Imperil need less mitigation reduction for monsters to reach 0 mitigation (and therefore less proficiency).
Elemental mages with Imperil generally encounter tough monsters with native mitigation resist of 66-68, reduced to 26-28 after Imperil, for which the player needs 0.68 prof_factor to reduce the 28 mitigation to 0.
Elemental mages without Imperil are doing it wrong.
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In general, regardless of element or style, you want to trade off as much EDB (in Phase) as you can, in exchange for proficiency cotton, until the average tough monster has less than 5 specific mitigation remaining (if possible). If you do the math, given the high amounts of EDB high level players have, you'll see that overall damage always increases by trading EDB for prof, up until the point where tough 68-mitigation monsters have had their mitigation reduced as much as possible.
Counter-resist and reduced mana costs from increased proficiency are nice, but they're only side benefits and don't matter enough to think much about, I think.
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That's when fighting ordinary monsters. When fighting SGs, it's a lot different, due to their very heavy resistance to elemental and their general lack of resistance to holy/dark.
And just to add more spam:
Effects
Magic proficiencies:
Lower the cast time and mana cost of spells by up to 25% (based on spell).
Increase the duration of sustained spells (beyond the effects of abilities).
This includes the duration of status effects.
Base durations can be found on the Spells page.
Durations can be increased by maximum a factor of 7 (supportive/curative spells) or 4 (everything else).
Increase a player's counter-resist and grants a specific element mitigation reduction with spells of that type.
Both effects depend on the player's proficiency factor, capped between 0 and 1:
prof_factor = (effective_proficiency - monsterlevel) / monsterlevel
Counter-resist bonus = prof_factor * 50%
Mitigation reduction = (prof_factor ^ 1.5) * 50
So going from 600 to 700 @ Level 500 increase your prof factor from 0.2 to 0.4
Cast-time/Mana-cost is linear reduction, so from 95% cast-time/mana-cost to 90%
Counter-Resist is also linear, going from 10% to 20%
Finally the non-linear Spec. Mitigation reduction, you go from 4.47 to 12.65
So costs/time experiences a 5.26% reduction in overall cost
Counter-Resists (ignoring the triplicate counter rules) experience an 11.11% reduction
Spec. Mitigation reduction has a varied effect dependent on monster/imperil ranging from no effect if it already hit zero or negative to an increase damage of 27.76% at 75 spec. mit and no imperil.
Adding imperil imperils the entire results so is ignored here due to it having its own casting cost/time, and impacts spec. mit.
1000 (max) prof gives extraordinary benefits. Not enough for the math to pan out though. Capped prof gives 25% cost/time reduction, up to 50 specific mit reduction (almost no need for imperil against spec mit, too bad magical mitigation not impacted), and 50% counter resist (beats the 10% on staffs base).
TLDR: Super got the same result as my spreadsheet, about 2 pieces is enough.