edit: I've run some sims, the transient int from PT/LW is still worth a little more than HS/DG
I'm curious what the current state of this is. It changes with item level - mp5 per int gets lower and lower with a higher gearpoint, and mp5 per spirit goes up by a lot. It's why I'm bringing up this long dead topic that had a pretty clear answer in 4.0.
PT and Lightweave both seem to average about 130 int.
Heartsong seems worth 180 spirit (very high uptime), and I can't find reliable numbers for darkglow. Probably about 130 comparing the tooltip to Lightweave.
So, which is better? Averaging 260 int on procs, or averaging 310 spirit from procs?
On one side, int procs weigh in less for holy than disc. Passive regen plays a much larger role. For disc, the benefits are throughput + active regen, so it's a no brainer to use PT/LW.
SpiritRegen(SPI,INT,LEVEL) = (0.001 + SPI * sqrt(INT) * BASE_REGEN[LEVEL]) * 5
dR/dSpi = 5*base*sqrt(int)
dR/dInt = ( 5*base*spi ) / ( 2 * sqrt [ INT ] )
dR/dSpi = 5 * 0.003345 * sqrt ( 6999 ) ->>>>>>> raidbuffed
dR/dInt = ( 5 * 0.003345 * 2300 ) / ( 2 * sqrt [ 6999 ] ) ->>>>>>> raidbuffed
dR / dSpi = 1.40 ( mp5 from HS+Darkglow = 434 mp5 )
dR / dInt = 0.23 ( mp5 from PT+Lightweave = 60 mp5 )
So, Heartsong and Darkglow have a significant edge on mp5 unless you can time shadowfiend with PT and LW. Consider also they're unlikely to proc near the same moment except right at the beginning of the fight. Even then, you have an extra 1080 transient int, which is an extra 16k mana. 30% of this is ~5k mana, and in a 5 minute fight that's another 80 mp5 from shadowfiend for a grand total of 140 mp5, if you can make all your procs line up. It usually won't happen, so you're more likely to use fiend with only one proc active which would make the two enchants worth 100 mp5.
It's not enough to say, really, because int procs improve efficiency. By how much? Maybe 3-5%? Does that make up the difference? is 4% overall efficiency worth losing 330 mp5? Maybe, but it's hard to think about. Same 5 minute fight that extra regen counts for 4 extra PoH. I think I have to see some logs from a holy priest in 25 man, at about my gear level, to see if that's enough.
Any thoughts on this? I might have to start playing holy again soon.