I copied a premade, and was testing out some dps in darnassus running at 59 ms. With procs and trinkets I have 1020 haste, which increased casting speed by 33%. I saw no increase in casting speed. Mind flay , mind blast, mind sear, and vt all took the full time to cast.

I searched the forums, but found nothing on this, although I didn't look for a long period of time.