Infraction: 3. All discussion should be both polite and civil.
Message to User:
Although neither of you are 100% right about the haste formula, being civil is nice.
None of the above.
The 4x set bonus reduces the base cast time of the spell (after talents are applied), from 2.0 to 1.8. After this point, haste is applied. So final cast time will be calculated as 1.8 * (100 - haste_percentage/2).
That's plainly wrong, haste is not calculated like this. Just take 50% haste for a spell with base cast time 1.5s. It should give a cast time of 1s whereas your formula wouldn't give that. Or even more obvious, 200% haste would give a cast time of 0s. By the way, however wrong you formula is, it still complies with my formula : you're just multiplying your old cast time by 0.9, so you're making two mistakes in your post.
As for the way the 4p bonus is applied, how do you know that it reduces the base cast time and not increase your haste value ? If you don't know how haste works, I highly doubt your statement has any valid ground. The only way to check is to remove a T11 item without haste and compare the cast times. Unfortunately I don't have 4p T11, so could someone give their numbers ?