Maybe its asked and replied but its hard to search the forum for specific questions.
I have around %28 haste and have the metronome and dark whispers. Oneth's and Fel ring for legendaries.
Bloodlust is usually given on combat start or a specific time. Especially if its at start Whispers in the dark and metronome procs and you get GCD capped with very high haste. Also if you pop CA/Incarnation your haste increases with each cast further.
So is it a better idea to wait until bloodlust finishes and pop CA/Incarnation for a more consistent damage output and to avoid being GCD capped? I do have the Fel Impeccable ring so its always wise to pop CA as soon as possible to get max. value out of it. But being way over the GCD cap for as much as 15-20 seconds looks counter productive at real combat.