I played around a lot with haste numbers & DW numbers years ago and as I've got older I've not practiced math in anyway, but, The total cap on Haste is 80%, DW is applied seperately (meaning it doesn't stack). There is I believe a total delay reduction cap much like their is straight cap of 80% haste on haste which is reached fairly easily with equipment (25%) Hasso OR Haste Samba (10%) leaving the final 45% to come from some combination of Haste, Haste II, Bards Marches and any other magical haste haste.
You can receive 80% Haste on NIN and still then receive the delay reduction Dual Wield gives. A Nin could fairly easily attain 54% Dual Wield from Job Traits(35%)+Reforged AF body(7%)+Reforged AF2 legs(7%)+the good ol Suppa(5%). Once you start getting delay reduction above 50% the benefits really start to show, its also worth noting that on Ninja, to attack the fastest you can equip use the delay reduction you can stack the most of for DoT Damage, so with some basic equipment thats 54% and can be reached on your own. To get above 50% haste you need haste from other sources.
Its also worth noting that there is an overall cap on delay reduction, that before was fairly hard to hit, i'm not so sure now, and that includes the delay reduction from Haste + delay reduction from Dual wield + the delay reduction Blitzer's roll (that to my knowledge does not stack with dual wield).
Basically, we don't have the guys working all the best equip sets out anymore, comparing piece A to piece B or C for TP-ing in, yes there are damage calculators, but I wouldn't put my trust in those unless they have been updated with ilevel additions.
Firstly, it would be good to know if there is a cap on Dual Wield, because if it is something low like 50% that would be a bit of a shame. Secondly we need to know the total possible delay reduction attainable because it might be able to be worked out that NIN could hit that fairly easy with the gear available to them /DNC with a trusts 15% haste spell, or Ulmia etc. The thing is, with the speeds NIN can potentially reach it could be easily on par with MNK for DPS, but that depends on what the total delay reduction is, and any caps in place on Dual Wield.
I remember the ls chatting about it saying the lowest delay a weapon can swing at is 75- That doesn't sound to bad because when Dual Wielding all delay reduction is applied to the total delay of the weapons, is 75 delay is the fastest we can reach then would that mean a nin could potentialy swing with 2 37.5 delay weapons?
Need a math guy who knows exactly what he is talking about to help this thread out.