Mana regen enchants are a bit of a waste of time due to the rather stupid nature of the regen rates in combat.
What combat? With the right perks, a sturdy aggressive follower, and good mana regen you can keep 2 Dremora Lords active, and thereafter never engage in actual combat, even with mobs and bosses.
That's how my Breton got built anyway.
Just pumped magicka, conjuration and conjure spell-cast reductions, and picked up cast reduction and mana regen gear.
I could survive well enough wearing Archmage robes with a good 2-hander and 2-hander perks, popping the occasional health potion,
and/or retreating.
Just didn't have to once I could keep the 2 Lords active.
Never even used destruction spells unless the game required it.
I did get to see my Erandur and Atronachs use it often before I got to the Lords.
Not recommending that, just how it worked for me.