More to the point I think people are way too caught up in the whole "stack these stats" mindset, that's not how you get the best gear possible. If you want to see how good an item is, what you do is simply multiply the amount you get from each stat with the DPS value of that stat, and add them all together for a total value. Mindlessly just taking anything with haste on it will end up with you doing a lot less DPS than someone who actually checks the real value of their gear.
Saying "I'm going to go for [x] amount of haste" is a somewhat silly thing to say unless there's a significant softcap at that point (frankly, those hardly really exist for warlocks)- you'd be better off just judging items by their DPS value relative to your current gearset than you would be by aiming for a certain amount of specific stats.