I've been having this discussion with several people in and out of guild and none of us can quite seem to agree on this issue.

I have 55 passive spell haste, and if my Scarab of the Infinite Cycle procs (giving me an extra 320), it lowers my Flash of Light cast time to 1.27 seconds. Logic would dictate that I would be clipping the GCD on every cast if I'm casting with less than 200ms ping. I've been testing this out in Shattrath for the last half hour, and I haven't clipped the GCD a single time when my scarab procs.

Has anyone else done any research or had any concrete facts regarding whether or not spell haste actually lowers the global cooldown or not? From what I am seeing here, logic would dictate that it does because I should be getting "GCD owned", so to speak, when my scarab procs.

Thanks.

I use a Mystical Skyfire Diamond, which lowers many of my spells from 1.5s to .75s casts, and haste definitely does not affect the GCD.

I'm pretty sure the meta gem works differently, as in it doesn't actually give you spell haste rating.

I'm fairly certain you are incorrect. For all intents and purposes, Mystical Skyfire Diamond gives you 1050 spell haste rating for the next cast within 4 seconds.

Here is my attempt to explain the situation:

All of your spells are initiated manually: You decide when they start, and they automatically go to completion x seconds later. If you are a button masher, you will mash your flash of light button at most maybe 4 times a second, meaning that no matter whether you have 0% haste (1.5s FoL) or 15% haste (1.275s FoL), you still initiate spells at discrete intervals, and since both cases could fall under the same 0.25s interval, you might not see any benefit from haste.

If you aren't a button masher, well chances are you just aren't pressing your FoL fast enough to truly benefit from your haste. That is why spell haste is so flawed compared to melee haste.

It has been determined (see Working Theories of Theorycrafting in the Class Mechanics forum) that spell haste does not lower the GCD, but that bloodlust and heroism do lower it. I do not know, however, whether the meta gem counts as spell haste (and thus has no effect on the GCD) or whether it falls into the bloodlust/heroism category however. (I would guess the former but I don't have a character with the meta with which I might go about checking.)

If you click on any of the 'Similar Threads' at the bottom of this page, they all seem to agree that the GCD is unchanged by haste.

I also came across this thread yesterday, with some actual screenshots of hasted sub-1.5 second spells running into the global cooldown and failing. Bloodlust and global cooldown

Thanks for the replies guys. Checking my combat log down to the millisecond seems to confirm what you guys are saying.