I timed a friend's Mithril 2-handed sword last night
(40 delay, permanent haste).
Mith 2H Time Swings Delay %chg Delay %chg Speed
Base - - 40.5 - -
Normal 30.7 10 30.7 -24.20% +31.92%
Anthem 47.2 20 23.6 -41.73% +71.61%
So it would seem haste weapons are working the same way. A
base 30% haste, but add any spell/song and you get the max
haste (somewhere between 70%-75%).