A fully melded set with tier 4 accuracy gives you +162 accuarcy, so you get to 516 accuracy (around A2S acc cap).
A fully melded set with tier 5 accuracy gives you +216 accuracy, 570 accuracy (around A6S acc cap, from what i know).

Still wish we could get some accuracy on gear so we at least don't miss on snoozefest dungeons without melds. Additionally, any materia bonus you might have will get ignored in any level/ilvl synced content.