Vengeance DH Global cooldowns and haste?

Greetings. Can someone explain to me how haste affects GCD for vengeance demon hunters and what the cap is?

Is it possible to speed up the global cooldown for sigils or spirit bomb for example?

Get Haste to around 30% and that will smooth out your rotation. From there you can add or remove Haste to taste.

Currently I believe there’s no real cap on Haste, but pushing much past 30% isn’t really necessary.