I made one AGES ago so keep that in mind -- but as i recall, you need 120 ias in weap to hit 5 fpa. This means that your options are basically naga or dimensional blade, which both have a base speed of 0. Naga has higher damage output, but also has much higher stat requirements.
Im pretty sure i also used crafted 10% cb gloves on the char. You don't need any further ias from your gear and crushing blow helps to boost overall damage output. More importantly though, crushing blow also helps with "stun locking" as it puts your opponent in a fhr animation.
You should try testing the build in single player