Effect of Attributes on Weapon Damage Attribute
Level Percent of
Weapon Damage
0 - 35.6%
1 - 38.6%
2 - 42.0%
3 - 45.9%
4 - 50.0%
5 - 54.5%
6 - 59.5%
7 - 64.8%
8 - 70.7%
9 - 77.1%
10 - 84.1%
11 - 91.7%
12 - 100%
13 - 104%
14 - 107%
15 - 111%
16 - 115%
As an example, if you had a normal, customized (20% more damage) 15-22 damage Dragon Sword, and a level 9 Swordsmanship attribute, each swing with the weapon would deal:
15 × 1.20 × 2(( 5 × 9 - 60 ) / 40) = 13.88 minimum damage
22 × 1.20 × 2(( 5 × 9 - 60 ) / 40) = 20.36 maximum damage
While swinging the same sword with a level 12 attribute would deal:
15 × 1.20 × 2(( 5 × 12 - 60 ) / 40) = 18.0 minimum damage
22 × 1.20 × 2(( 5 × 12 - 60 ) / 40) = 26.4 maximum damage
While pumping up your weapon attribute continues to give outstanding, exponential returns on damage all the way to level 12, it drops off quickly after that. Attribute level 13 is less than half as effective as the previous level at raising your damage, and attribute level 14 is even worse. So while having a level 13 or 14 attribute might look good on your stat screen, it isn't doing a whole lot in game. You'd be better served lowering that attribute and investing elsewhere.
More information at
http://www.guildwarsguru.com/content...nics-id674.php
All credit above to Ensign.