Combat Regen (per 5 sec) = (Total Mana*0.02) + (1.1287*SPI*Meditation%)
Combat Regen at Level 90 = (300k*0.02) + (1.1287*SPI*0.5) = 6000 + (0.56435*SPI)
Epicurean:
Passive gain = 0.56435*300 = 169.305 mana per 5 sec
Rapture gain = 300*1.5 = 450 mana per 12 sec (187.5 mana per 5 sec). Highly improbable to get Rapture exactly ever 12 seconds, so this number is skewed higher.
Passive + Rapture gains = 169.305+187.5 = 356.805 mana per 5 sec
Arcane Torrent:
Returns 6% of total mana (18k at level 90) every 2 minutes. If used on CD, that's 9k mana a minute, 750 mana per 5 sec.
With Hymn of Hope, total mana would reach 345k, yielding a 20.7k mana return with Arcane Torrent (862.5 mana per 5 sec).
If I'm not stupid in terms of my math, then Arcane Torrent is the clear winner from a mana regen standpoint. Please correct me if I'm wrong.