Optimal rank gear

I was under the impression that because of the way optimal rank on gear worked, at a certain point. You benefit more from wearing gear that was above your rank, because it will either 1) Give you the same amount of stats, or 2) Give you MORE stats than gear that is below, or at your optimal rank will. (Of course it will break faster though. but that being the ONLY gimp)

but I have heard from a few people that wearing gear that is above your optimal rank affects things that cannot be seen in stat numbers. In particular being affecting your synthesis success rate (OTHER than craftsmanship).
Is this wrong?