Wanted to give some updated numbers in reference to my test to find out if MND is an additional modifier for Holy Succor. The two gear sets I have been using are 337 MND with 428 Healing Magic Potency. Let's just call that the MND set. And 288 MND also with 428 Healing Magic Potency will be the HMP set. All other stats remained unchanged between the two gear sets.

50 casts of Holy Succor with each gear set: With the MND set the range was 876-923 with an average of 894.68. With the HMP set the range was 852-903 with an average of 878.69.

50 casts of Cure with each gear set: With the MND set the range was 468-497 with an average of 478.41. With the HMP set the range was 470-497 with an average of 478.72.

I would have liked to get those sample sizes closer to 100 with each set to have a little more statistical significance and less margin for error, but unfortunately I had other things to do this evening. What was very obvious over the course of the 100 casts I did make was that the MND set had a higher ceiling and a higher floor for Holy Succor, but the difference between sets for Cure is statistically insignificant.

I feel confident is saying that I believe MND is an additional modifier for Holy Succor. Ultimately Healing Magic Potency is the biggest determinant of Healing Magic, but at least in the case of Holy Succor, adding MND seems to enhance it's potency even further.

Like stated above, MND seems to be the most effective stat overall for PLD. And as Treach stated above, the benefits of MND on AA likely caps around 305-310. I have yet to test this as well, but so far the most effective DD build I have made for PLD has been with approximately 300 of each MND and STR. Using the MND build above with 337 MND required me to drop my STR to approximately 245 by removing gear. My normal solo build is 284 STR and 307 MND. In dropping STR and boosting MND to 337, AA and WS dmg dropped noticeably.

So for those seeking the most effective DD build, STR and MND in a nice balance as close to 300 as you can get each will be most effective as Treach infers above. It takes double melds and maybe a triple here and there to get both near 300, but it is doable. It's actually easier to do on GLA because you have that extra 10 STR instead of VIT when on PLD.