Windmill Prolonged Spin or Extra Dmg?

I was wondering as far as windmill is concern, what would yield more damage.


Adding the +15% Additional DMG Perk

or

Adding the 25% Longer Duration Perk.


Can anyone figure this one out?

as what i observed a 25% duration upgrad windmill has 3spins without it, it only has 2spins.

means it makes 3dmg per cast.

just do both