I've parsed a miss when I was at 536 accuracy on my PLD in Turn 5. I don't think that means the acc cap is above that. What it probably means is that once you hit around 472 acc, you have a 99.99% chance to hit. (The game might not let you get 100% accuracy)

Ever since then I've been running with 475 acc and I a 100% hit rate so far (for over a month).