I have a great computer, never any problems with anything else, run 70-110ms max, run on all max settings, same with WOW. I never get any stuttering, or any problems in general except something in the last few weeks.
In Rakkis Crossing, after you past the door to the cellar store, you head up some stairs to the next section and there is always a ton of fire and a ton of mobs. EVERY single time i get a huge lag spike once i start CM/WWing. Doesn't matter if I play single, or with group play, it just a huge lag spike and slows and I usually end up dieing. Second time, everything is fine.
Seems like this is a common issue for wizards: