Question about Vital Strike and Devastating Strike

[8 Red Wizards]

This feat is in Ultimate Combat

Devastating Strike (Combat)

Pitting all of your strength and resolve against your enemy,
you deliver a strike that is impossible to ignore.

Prerequisites: Vital Strike, base attack bonus +9.

Benefit: Whenever you use Vital Strike, Improved
Vital Strike, or Greater Vital Strike, you gain a +2 bonus
on each extra weapon damage dice roll those feats grant
(+6 maximum). This bonus damage is multiplied on a
critical hit.
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My question is if you are using a Great Sword with Vital Strike, Improved Vital Strike and Greater Vital Strike. Would the damage of all the combined feats be 8d6+6 or 8d6+18?

[Glutton]

+6

[truesidekick]

just a sugestion, i know vital strike seems like a good feat, its really not. they have much better choices out there besides vital strike.

the only exception i would make to that is if you were going barbarian for furious finish build for big hits. even then you usually do more damage with a full round attack and/or pounce.

[Lune]

Or if you are a druid wild shaping into something with one big attack. Like a Allosaurus.