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
240 haste = 4 set
160 Crit = 4set
120sp = 4set
Note that this is just estimates in my head if someone wants to figure out correct values they can.
1 Spellpower = 1 Spellpower
1 Crit Rating = .8 Spellpower
1 Haste Rating = .50 Spellpower
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.