Haste rating
Haste rating normally only effects the speed at which you cast spells and the duration of your global сooldown. However with Glyph of Quick Decay it will also make your corruption tick faster. Haste Rating scales multiplicatively with other sources of haste- and haste can not reduce the duration of a global cоoldown further below 1.0 second. This means that once a spells cast time or global соoldown is reduced to 1 second, additional haste will no longer benefit those spells. To gain 1% spell haste from haste rating, you need 32.790 haste rating.
Because haste rating benefits all of our spellcasts and is a relatively cheap stat, it is typically either the best or second best stat for spellcasters- for demonology Warlocks it is a great stat for personal DPS (only beaten by Spellpower), however takes the back-seat to spirit when raid DPS is considered (Demonic pact in particular).
While it is possible in ICC gear to get so much haste that we push our global coоldown back to 1.0 seconds, the lion-share of our spellcasts are longer than 1.5 seconds, and as a result stacking more haste even beyond that point will still provide goоd DPS returns.
The formula to calculate the 'new' cast time of a spell is as follows:
1. New.Cast.Time = \frac{Normal.Cast.Time}{Casting.Speed}
The default casting speed is '1', this number should then be multiplied by all haste effects in the following way:
(In this Formula we use 950 Haste rating as an example)
Wrath of Air (5%), Improved Moonkin Form (3%), Haste Rating / 32.79 (%):
2. Casting.Speed = 1 \times 1.05 \times 1.03 \times (1+\frac{950}{3279})=1.395
To now calculate the cast time of a spell using the previously calculated casting speed, simply use the formula above:
3. Cast.Time = \frac{2.5}{1.395} = 1.792
(In this Formula we use a 2.5 second cast time as an example)