Hi,
Here some maths i got from several sites:
Casting speed - WoWWiki
This can be found in several forums:
Haste Cap:
Original Casting time /(1+Haste in percent) = Real Casting Time
The GCD, before haste, is 1.5 seconds.
1.5 seconds / (1+X) = 1 second, where X is equal to 50% Haste
1% Haste = 32.79 Haste Rating
50% Haste = 1,639.5 Haste Rating = Haste Cap
Raid Buffs
Wrath of Air Totem = 5% Haste
1.5 / 1.05 = 42.9% or 1,406.7 Haste Rating to cap.
3/3 Improved Moonkin Form = 3% Haste
1.5 / 1.03 = 45.6% or 1,495.2 Haste Rating to cap.
Both WoA & ImpMF:
1.5 / (1.03*1.05) = 1.5 / 1.082 = 38.6% or 1,265.7 Haste Rating to cap.
Bloodlust
1.5 / 1.30 = 15.4% or 504.97 Haste Rating to cap.
WoA, ImpMF & Bloodlust:
1.5 / (1.30*1.03*1.05) = 1.5 / 1.406 = 6.7% or 219.69 Haste Rating to cap.
Talents
Eradication
1.5 / 1.20 = 25% or 819.75 Haste Rating to cap.
Backdraft
1.5 / 1.30 = 15.4% or 504.97 Haste Rating to cap.
So there was an discussion at the ensidia forum, where I asked the same question:
The Haste Cap - Ensidia
Still I have to figure out what the ideal soft cap is: Is it 504.97 or (see endisia thread) 757 haste rating