I'm seeing a lot of posts lately about these two issues and since they are closely related i'll make a little guide *FROM MY OWN RESEARCH AND OBSERVATIONS*
Ethos: I am currently rank 20+ as conjurer and have spent time detailing Optimal Rank with exact numbers.
At 1 Durability, Skill gain is cut by 50%
Below 50%, Accuracy and Damage are reduced.
Below 50%, Damage Reduction is reduced.
On weapons, Optimal affects Accuracy and damage which in turn affects skill gains.
I tested both rank 11 elm cane vs rank 22 willow wand.
At rank 13, the willow wand was 12 points worse in each stat(damage & accuracy). There was also a hidden accuracy debuff that I am theorizing because I noticed a much higher miss rate. I tested this with the weathered cane level 1 which had worse accuracy than the rank 11 elm cane, but I hit more with the weathered cane than i did with willow wand at level 13.
At level 14, the willow wand did not increase, but at level 15 it gained +3 points in damage and accuracy, and continued to do so until level 18. At level 18, rank 11 elm cane and rank 22 willow wand were equal, but I still experienced a diminished accuracy AS WELL AS a higher rate of durability loss. At level 19, the willow wand had higher stats, but lower accuracy still, at 20, I noticed that the accuracy was normal and at 22 I hit the full stats.
The exact variables changed as I increased in level obviously, but I did write down that at level 14 against Aldegoat Nannys, I was averaging 45 skill per attack. I also only tested exp with spirit dart since spells have such random exp. After my weapon was broken, I was averaging 20-25 skill per attack. Same held true at level 18 against cassiopeia's. Averaging 50 or so with pine crook and when it reached one durability, was dropped to 20-25 range again.
My sample size was large enough to know it was not a fluke. I probably killed 20 or so mobs to make sure before going off to repair.
Using below optimal rank reduces the amount of stats provided and the damage reduction offered. The penalty seems to be less than weapons, but your durability will decrease faster.
Try to equip weapons the closest to your level. It really doesn't benefit you to equip a shiny high rank weapon, and it will be detrimental. Armor has a little bit more wiggle room than weapons, but Durability is lost faster so keep that in mind if you're out for a long grinding session.
I'll put this at the bottom as well because I know the reading habits of people on this forum - all of my information comes from:
*FROM MY OWN RESEARCH AND OBSERVATIONS*
Edited, Oct 5th 2010 11:51pm by xGaelx