Infraction: 1. All posters are to make an effort to communicate clearly.
Message to User:
This post was a little too much like a blog. Try to keep the questions focused, mathematical (if possible), and based on theorycraft, rather than anecdote.
In general, haste for a destruction warlock has some interesting step functions to it. If you're modeling just a plain immolate + incinerate rotation, you'd only get benefits from haste at the levels where you could fit in more incinerates per immolate, really. Having an extra 0.8 seconds after your final incinerate is kind of annoying - do you LT, toss a corruption? Clip immolate? etc.
So yeah, I concur - haste has a funny scaling system that is clearly not smoothly linear. On the other hand, you're frequently under multiple haste effects. Moonkin, wrath of air, heroism, etc, all change the calculation, so it's possible to argue that you should probably just stack whatever stat scales best for you and let everything else take care of itself. At the end of the day, though, if you don't have master conjurer, the bonus you get from either stone relative to the other is very small.
I have been looking for information on this very topic. I find that with my current haste rating of about 550 (unbuffed) I have time at the end of every other immolate where conflag and CB are still on CD and I don't have time to cast a full incinerate. This jumbling of the rotation is fairly annoying and sometimes I clip immolate (I'm sure everyone is aware they changed the mechanic of immolate not reapplying). I still don't want to clip immolate, but with my current haste I end up with dead time in my rotation.
I heard from someone that around 400 haste is ideal for deep destruction. I understand haste scales better in theory, but forgive my ignorance, but can simcraft account for immolate uptime, conflag CD's, backdraft, and the number of spells you can actually cast during immolate without wasting uptime?
TLDR: I'm thinking of dropping haste for crit to try and smooth out the rotation and hopefully increase DPS.