I find it worth mentioning the in combat mana regeneration is a is based off max mana.
I haven't tested too intensely, but mana is roughly 1.7% of your max mana a tick. This translates in to 60-ish mana to get one more mana a tick. This isn't a big deal, but it can help conjurer who doesn't get a mana regen skill until high levels.
I would of tested it more, but I frankly haven't accumulated enough piety gear.