It's still around 50ish% though. If I choose double durganized stilettos, like I have, and then plain clothing it says x1.43 faster, but if I choose plate it goes to x1.01 slower. I put 20 DEX in. What I did found out is that basically nothing stacks with DAoM pots, including gear like Gauntlets of Swift Action.
For Dual Wielding, whose recovery frames are higher percent value of their total delay, DAoM is more valuable than it is for an Arquebus, whose attack delay is spent reloading, rather than 'recovering' from the shot. DAoM seems it doesn't stack with lots of things because in a lot of cases it caps out your recovery frames at 0.
Without buffs, this also means heavy armor is, again based on percentage, most disadvantageous for a dual wielding build because the fraction of your attack delay due to recovery frames is the highest. But, since your attack speed is capped out at 0 recovery frames - once this capped is reached, Plate is always better than Cloth because it offers all of the benefits (Beefy DR) without the major negative of recovery.
The main takeaways are: Plate is NEVER a true 50% less attack speed modifier due to the way recovery frames works. If you use lots of buffs every fight, Plate is excellent because you will hit the attack speed cap very quickly. An example of this is a Barbarian dual wielding Stilettos with Frenzy, Bloodlust, and Two Weapon Style using a Durganized Plate Armor is at 1.57x faster, where the cap is 1.69x faster. When you look at it, Bloodlust, Frenzy, and Two Weapon Style are pretty Vanilla in terms of buffing a Barbarian, and is something he'll have for the vast majority of fights from approximately level 7 onward. Another interesting thing about Barbarians is the talent Bloodlust, which removes recovery altogether if he lands the killing blow...which he'll be doing a lot with a properly built Carnage. Plate increases recovery by 50%, but Bloodlust completely removes it from the picture - aside from bosses where he won't be getting a kill every swing, why would you NOT use plate in this case?
If you build Durance using an Arquebus (which is a great idea because of his +10 Accuracy talent, Priest hasshitty base defenses, and it'll keep him safe to cast those spells faster), regular Plate and no modifications to his speed is only 1.01x slower than naked shooting.
This also suggests not to use your very limited Durgan ingots all on one character if you know they spend most of their time in a fight buffed. In PoE, Plate armor is actually too damn strong. On PotD where fights are long, and you get outnumbered this is important.
Note: All of my numbers are done using 10 Dex - upping your Dex closes the gap even further, because of a natural recovery frame decrease.