Somebody did the math on this in another thread here @ ZAM, but I'm too lazy to go find it. If I recall correctly, wearing an item for which your rank is below the optimal rank results in the following:
~ you get some % of the base stats for the item (Def., Mag.Def., Eva, Res)
~ you DO NOT receive any of the bonus stats until you reach the optimal rank
Example with made up #'s:
So if you are lvl 5, and you wear gloves that are optimal rank lvl 8 with these stats: def 10, mag.def 10, eva 10, res 10, +2 acc, +2 str, you would get the following stat bonuses: def 8, mag.def 8, eva 8, res 8, but no bonus to acc or str until you hit rank 10.
That's how I think it works and what somebody else parsed it out as. So don't xp in gear that looks cool and/or gear that you wanna show off b/c sometimes you get better stats from an item with an optimal rank 7 levels below your current rank rather than an item that is 1 level above your current rank.
Edited, Oct 15th 2010 10:23am by DonFlamenco