Hi Armok,

Yes, even 1 or 2 ranks below your Optimal Rank will have a negative effect. When you hit "Optimal Rank" that's when you get full benefits of the stats of the item you equip.

I don't know the exact %, but I tested out a few items, and was surprised that even just 1 Rank below Optimal Rank, and I was getting less of a boost than my previous equipment that I was already ~9 Ranks above.

I think that's one of the flaws of the current system: It allows a lot of freedom (anyone can wear anything (except the newest items added recently under Yoshida-san that "requires" a class), but at the same time, many may not even realize that they're taking a sizable Penalty Hit in terms of Stats.

Then again, everything is quite easy at the moment, so you can have people wearing Crafting Gear and still go out and do Battle Guildleves and get by just fine.