A. Base Regen
As a traditionally "spirit based" mana regeneration class. The level 80 version of the mana regeneration from Int and Spi now follow the following formula's:
oo5sr = 0.016725 * Spirit * SqRt(Intellect)
i5sr = oo5sr * .17/.33/.50 (Based on the points in meditation. 3/3 Meditation is standard in all specs.)
This portion of the mana regeneration model is the only reason for Discipline to utilize Spirit at all.
Rapture had a major overhaul with the 3.1 release. It was quite imbalanced in its previous incarnation, though the current mechanic has some issues. Rapture provides 1.5/2.0/2.5% of total mana when a PW:S is completely consumed or dispelled and can only occur once per 12 seconds.
The maximum regeneration from Rapture is:
(Mana Pool) x Return% / 12 * 5 = X mp5
The maximal return is unrealistic and should instead be evaluated based on the amount per proc and the proc rate received. Instead you find that:
(Mana Pool) x Return% / 12 = X mp5 per proc, where the proc rate is from 0-5 proc’s/min.
21568 x 2.5% / 12 = 44.93 mp5/proc... The PTR proc rate data I was running was ~3.4 proc/min. So this would indicate ~152.8 mp5.
There needs to be more data collected and theorycraft analysis on the proc rate. The proc rate depends on multitude of factors. For a single target the proc rate is maximally 4/min based on the WS debuff. How close to this can be achieved is based on damage income and pattern, target avoidance, target mitigation..etc calculating an average “time to consumption”… Optimally a time to consumption of less than 3 seconds yields 4 proc/min.
1 Int = ~0.1538 mp5, maximally
1 Int = ~0.1045 mp5, 3.4proc/min
The mechanic behind Rapture indicates that PW:S should be used with regularity on any target that will benefit from being shielded and provides the potential or guarantee of the shield being completely consumed.
Replenishment is a talent available to a multitude of class/specs... The buff provides a 15 second buff on up to 10 people that restores 0.25% of total mana every second for the duration of the buff. Mental Strength couples well with Replenishment in a raid/group environment for Discipline.
1199 Int provides 17705 mana. That 17705 mana at 0.25% is 44.2625 mana per second or ~221 mp5. Based on the 221 mp5 @ 1199 Int you find that -
1 Int = ~0.18458 mp5 (not accounting Blessing of Kings or Mental Strength)
D. Mana Pool
The larger the mana pool the better the longevity over the course of the fight. This equates to mana regen based on the fight duration.
Mana Pool / Duration * 5 = X mp5, working with a 5 min fight duration at the previously demonstrated Int amount it works out too.
17705 / 300 * 5 = ~295.08 mp5
1 Int = ~0.2461 mp5 (not accounting Blessing of Kings or Mental Strength)
E. Spirit vs. mp5
The more Int the more valuable Spi becomes, though without a secondary benefit of having Spi it is a fairly weak stat for Disc. It takes approximately 3 Spi to equal 1 mp5.
Giving the opportunity Disc should choose quality mp5 gear over spirit.