base ed is nice, but it doesn't boost ar, or help meet stat reqs for claws.
expected damage per hit is a combination of ar and damage, so whether 20 dex or 30 ed is is better depends on your opponent's defense. if you run the numbers it's gonna be a wash. then add the fact that you need dex to use claws and it's ggs.
Pretty sure the helm can spawn with both dex and ed%.
Ed% being superior to the flat AR roll with a cruel claw.