Try using console command to find out -
getavinfo weaponspeedmult
(click on your character before entering)
Should tell you exactly how much each increases it.
Wiki implies that it's 1.3x(130%) for first, then increases by 20% to 1.5 then 1.7 for the third word.
Duration is 15 seconds regardless. Cooldown 30, 40, 50.
Seems to be a consensus that weapon enchants are a better option overall though.