I'm currently rank 27 wearing a rank 26 leather jacket. Current def: 224 current eva 254.
equipping a Rank 33 Leather harness (with both higher def and evasion) drops my def to 214 and raises my eva to 262. So there is definitely a negative effect to equipping gear too far from optimal rank. If you are rich and can stand the repair costs, at least make sure that high rank gear actually benefits you before using it. A rank 20 gladiator decked out in a full rank 35 set might actually have worse stats than a rank 20 gladiator decked out in a rank 20 set.
Actually no, your example is faulted a bit because Leather Jacket has higher DEF than Harness of the same rank. There are clothes/armour types and usually:
Cuirass > Haubergeon > Scale Mail > Jacket = Jerkins > Harness > Chain mail = Acton, consider the Def scaling with level because they are unfortunately not all of the same level.
The rest are not really suitable for Melee classes in term of DEF, that is, for everything we know currently. There bound to be other types of clothes we don't know. Edited, Oct 26th 2010 5:41am by Khornette