Clear Mind III increases your base MP regen to 21, and increases the increment between ticks to 2. What this means is that, unlike Clear Mind I & II(where you gain 15, 16, 17, for example), Clear Mind III you regain 21,23,25,27.
add a dark staff to that, and if possible a mages balladII and a refresh, this kind of regeneration even makes ancient magic usefull :P if only u had a bard and red mage along in every party :P
What i have done before, and it works very very nice, with almost no downtime at all. Is be a WHM/SMN with Auto-Refresh, and have Bard and a RedMage in the party. So I have Auto-Refresh, Refresh (from RDM), and x2 Ballad (from Bard). Now that is very nice MANA, i would add some Juices, but the Refresh from the RDM kinda overlaps that. lol...