Just got Ninja Body, Hachiya Chainmail
I tried to test the amount of DW using TP return.
This is the setup I used:
1) Completely naked (to avoid STP, DA, and whatever else
2) /BLM (to avoid specific DD traits that would alter my TP return, and to warp back faster!

)
3) Was standing turned around most of the time, then turning around to perform my tp round (to avoid parrying)
4) Was keeping shadows up to avoid getting hit (and gain TP)
5) Used Dynamis Katana (1 damage, 999 delay) and Senjuinrikio (dmg 25, delay 227).
TP return without body:
20 40 61 81 102 122 142 163 183 => 20.4 TP per attack round
TP return with body:
18 36 55 73 92 110 128 147 165 => 18.4 TP per attack round
Does this mean the body gives 10% Dual Wield?