To add to this:
You can cap all those other pieces without using any grade IV materia. A single Craft IV materia will let you cap the chest piece as well, otherwise you leave a single point of craftsmanship on the table. Off hand is the only piece that can get significant benefits for using grade IV... and you have to overmeld everything past the first materia anyway.
One of the more amusing melds I saw from examining people in town was a chest piece with a Craft IV, a Craft III, and a Craft II with the other two overmeld slots not used. Was someone I've seen selling Titan runs, so I guess he had the money to throw away, lol. Had grade IVs in a number of other slots as well.