So after a great deal of debate on what DEX does, and the limited testing results we have from sources, I decided to spend today gathering some data for the discussion.
I ran tests with 5 different gear sets, registering 5000 hits per gear set. ( I actually did more, as it appears unless you are directly facing the mob, you lose a significant amount of parry, just fyi )
For simplicity, I used level 37 Wolfs near camp dragonhead. I could AFK on them with no issues, and they did not have any dot effects that would have skewed the numbers. Since Parry is a simplistic check, the value of parry % should not be a factor with mob level. I did have to do the math manually as the game uses a 1 hit skill check.
Test 1:
189 Dex
440 Parry
Registered 24.88% Parry rate.
Test 2:
216 Dex
456 Parry
Registered 23.19% Parry rate.
Test 3:
216 Dex
486 Parry
Registered 25.08% Parry rate.
Test 4:
246 Dex
486 Parry
Registered 28.63% Parry rate.
Test 5:
266 Dex
456 Parry
Registered 27.91% Parry rate.
Results Interpretation:
Contrary to the previous results given on the Methodology, it appears that the walls for DEX are much higher then the +-15 recorded previously. There is little to no difference between the first three tests, even with a 27 dex and 46 parry increase from test 1 to 3.
However, once hitting 246 DEX, using test 3's gear setup and +30 dex from attributes, we got a 3.56% increase in parry rate. I would interpret this as a +-1% for variable sake, so a marked increase of around 2.5% would be fairly safe.
Somewhere between 216 and 246 is a DEX wall that increases parry fairly significantly. I would posit that it is closer to 246 then 216, as even going up to 266 did not allow me to hit the next wall.
You can reach this cap by wearing 5 Gryphonskin STR/DEX accessories, and possibly reach the next wall with a few HQ Darksteel, most notably the pants allowing for 30~ dex to be melded onto them.
Someone else will have to do the math to see if they are worth it in EHP, but at this point I am now skeptical that Gryphonskin is BiS.