27/37 = 73%
Still a hefty amount of damage reduction
Plus, lets take a look at stacking agility vs stacking accuracy.
Agility: Gem is 4m and you will benefit in every fight versus warriors and assassins
Armour - No drawbacks for gemming/Not a main offensive item
Belt - As above
Boots - As above
Bracelets - Lose some DC but the agility bonus is decent
Accuracy: Gem is 7m and you will only benefit in PvP versus the rare occasion you find a sin or tao with 23+ accuracy
Necklace - Primary offensive item/Will have to juggle with DC and aspeed
Bracelet - Same as agility
Helmet - No drawbacks
Belt - Same as agility