In this guide, it is recommended to take the Revitalizing Primal Diamond (wowhead. com/item=76888) as a Meta Gem. Wouldn't the one with Int and increased Max. Mana be a better choice (wowhead. com/spell=107759)?
According to EJ, 1 spirit is worth 0.5625 mp5, so the 432 spirit from the gem are worth 243 mp5. On the other side, 2% increased maximum Mana would bring our Mana pool to 306k instead of 300k, so it adds 6k mana. Assuming you use your mana tea (glyphed) with two stacks every 10 seconds, you consume 12 stacks per minute, which is 48% of your max. mana.
0.48x6000 = 2880 additional mana in 60 seconds or 240 mp5, so the mp5 averages out, while 216 int are stronger than the 3% increased crit effect. Of course, you won't always be able to use 2 stacks of mana tea every 10 seconds, but in my opinion it's definitely worth considering for some fights.
Edit: Sorry for the links, had to screw them up due to forum restrictions.