To reach a cast time of 2.2 seconds:
Haste Percent: 5.07%
Haste Rating: 649
GCD Becomes: 1.32 sec.
Haste Percent needed without buffs: 13.64%
To reach a cast time of 2.1 seconds:
Haste Percent: 10.08%
Haste Rating: 1290
GCD Becomes: 1.26 sec.
Haste Percent needed without buffs: 19.05%
To reach a cast time of 2.0 seconds:
Haste Percent: 15.58%
Haste Rating: 1994
GCD Becomes: 1.2 sec.
Haste Percent needed without buffs: 25%
To gain an extra tick on Renew, Hymn of Hope and Divine Hymn:
Haste Percent: 12.50%
Haste Rating: 516
Formulas:
Cast Time = Base Cast / ((1 + haste%/100)*1.03*1.05)
Flip this around:
Haste % = (Base Cast/ (Cast Time * 1.03 * 1.05) - 1)*100
128 haste rating = 1% haste
(2.2)
Haste % = ((2.5 / (2.2*1.03*1.05) - 1)*100 = 5.07% = 649 haste rating
(2.1)
Haste % = ((2.5 / (2.1*1.03*1.05) - 1)*100 = 10.08% = 1290 haste rating
(2.0)
Haste % = ((2.5 / (2.0*1.03*1.05) - 1)*100 = 15.58% = 1994 haste rating
GCD = 1.5/(1+13.64/100) = 1.32 sec
GCD = 1.5/(1+19.05/100) = 1.26 sec
GCD = 1.5/(1+25/100) = 1.2 sec
Taken from our Holy Guide sticky written by Mazi
http://www.mmo-champion.com/threads/...uide-%284.2%29