So! In geeky math terms:
Let F be the damage absorbed by Stoneskin:
[IMG]http://images.wikia.com/wikitex/images/0/07/072/6ef43c05ef0a556f59c5ac8fce6741.png[/IMG]
where X = (Enhancing Magic Skill/3) + MIND
(Formula found on http://wiki.ffxiclopedia.org/wiki/Stoneskin)
Does this mean that wearing a Promise Badge with Mind +5 while casting Stoneskin will have a more beneficial effect than wearing an Enhancing Torque with Enhancing Magic +7? :O