the ratio of MND to healing magic for cure III is as follows:
1healing potency has the same rough effect as 2.6666667 MND
This is in a 100% healing mentality, if you take into affect the desire to cast some enfeebles and might value some extra magic accuracy then the value of MND goes up even more.
If that was right I should have lost 2 heal potency when I removed a piece of +6 mind gear but instead I only lost 1 (and then lost another when removing a +2)
From the testing I've tried out so far it's between 3-4 mind per 1 heal potency. (Higher than 3 but no higher than 4)
I still haven't tested out too much with the M. Accuracy yet though so I dunno if it's the same ratio or not.