Before MoP was released, Sylvela (user @ MMO-Champion) did some rough maths on the potential mana gained from Ember Primal Diamond vs Revitalizing Primal Diamond (the meta gem most of us use).
The problem with these calculations, was that he/she assumed that a 2 stack mana tea could theoretically be used every 15 seconds but in reality, consuming a total of 8 chi for those 2 stacks of mana tea in a period of 15 seconds is a difficult condition to meet because of the gcds required to generate 8 chi and consume them and the fact that quite a few encounters have downtime meaning less healing required and less chi generated.[Ember Primal Diamond] - (3360 Mana Every Minute)
Keep in mind the variables, such as the Mana Tea usage, as this is what directly affects the mana regeneration for this gem. The value shown above is if Mana Tea is used on average every 15 seconds.
Gives you 480 additional Mana per 2 stacks Mana Tea (Glyphed)
It has a 10 sec Cooldown, I assume the player is using it every 15 secs (4 times per minute).
4*480 = 1920mana per minute
If you manage to use it everytime the cooldown falls off you will get:
6*480 = 2880mana per minute
But it also affects the manaregformula:
Which means that you get 120 mp5 (=1440 mana per minute) bonus from the total mana.
[Revitalizing Primal Diamond] - (2928 Mana Every Minute)
According to the regenformula for level 90 (thanks to Icy Veins!):
1 Spirit = 0,56435 mp5
You will get 244 mp5 from the meta gem.
244*12 = 2928 mana per minute
My question is, with the changes to crit being able to affect our mana tea stacks, it will most likely be possible to consume a 2 stack mana tea on average every 15 seconds, perhaps even a lower average, so will this meta gem be the better choice for mana regen?
Or, is the 3% increased critical effect from the 2nd meta gem too precious to lose?