Max Out DW

Im no NIN, but it seems like this would be nuts.
Use Atma of the omnipotent to cap gear haste

Or you could just get marches.

Because everyone has a bard following them all the time.

Seeing as the normal 26% 50 DW + haste already comes close to reaching the delay cap, there's no reason to using that set.

Pretty sure brutal would still beat iga earring (assuming it's 1%). You're also giving up a lot of crit rate/AGI or 15% TA to use this. Probably not optimal.

But, for clarification, you'll swing roughly 12% faster, with just haste spell using the OPs set. You'll swing faster in an unbuffed situation, probably less DPS though due to all the sacrifices.

can get dual wield +5 from synergy augments for shura legs

Dual Wield V
Obtained:
Ninja Level 85
Delay Reduction: 35%

Iga head +2 : 5%
Suppanomimi: 5%
AFv1 : 5%

35 + 5 + 5 + 5 = 50%

Isn't it the cap?

I always thought it capped at 50% as well. But assuming it doesn't, it's not worth to go past that anyways.

Yup especially when your getting more dual wield gear over double attack/haste. twilight belt + brutal earring (haste+7% double attack +7%) is far better than dual wield +10% (you're losing TP/hit here)
also leaving tiercel, and add Iga legs +2, will grant you to the cap easily, you could add Iga Neck with Quimirz thatlum and kamome it's +30% critical hit damage (and with Razed Ruin, it's even more).