Originally Posted by Rob

When your hasted, flurried weapon speed drops below 1.5, it is theoretically possible to do less damage than if it was above 1.5 due to the fact 3 swings will not be eligible for WF to proc instead of 2. However, if haste drops you below 1.4 your damage should pick back up again. As far as applying this theory to current itemization, this appears to mean that you primarily just need to be sure that passive haste + flurry + Mongoose doesn't push you under 1.5, because large haste procs like DST and Dragonstrike, and large haste use effects like Bloodlust and Haste Potions will be large enough to increase your DPS no matter where you are on the Haste curve (for example, if your weapon speed is 2.0 and Heroism pushes you down to 1.43, that's still going to be a net DPS increase even though you may lose some WF damage).