Assuming u have a nice haste plateau BEFORE 4set t8.5.
This is my own theory of haste, if u disagree go fondle with alternate(bad) theories at spriest.com
Code:
240 haste = 4 set
160 Crit = 4set
120sp = 4set
Code:
Basically
1 Spellpower = 1 Spellpower
1 Crit Rating = .8 Spellpower
1 Haste Rating = .50 Spellpower
Note that this is just estimates in my head if someone wants to figure out correct values they can.
So if you can get 120 Spellpower or 160 crit or a mix of both to make up for the haste loss u can make up for the 4 set.
2set t9 is worth around 100spellpower according to spriest.com which sounds about right, worth less depending on how much haste you have, tipping point would be around 400 haste.