I just received my 2.93 matte today and was a bit worried so really put this machine to its limits on the 9600.
All these tasks were running at one time: Cinebench, ripping a dvd at the highest quality in Handbrake, watching 2 movies off of an external hard drive, have that high rez image as my desktop, watching an hd 1080p Transformers trailer, watching a trailer of a movie in itunes, watching a youtube video, all while having about 10 internet pages open in Safari.
The max I could get the cpu to hit was 91 percent. The cinebench got it up there when it performed the dual processor test. With all of the above going on at one time, I could view all of the movies and trailers without missing a frame. No stuttering whatsoever! No green lines. Nothing. To top it off the computer isn't really that warm compared to my old MBP 15" 2.33. I was running at this intensity for about 20 minutes, but have been ripping a dvd for the last hour and a half while watching movies, etc.. Anyone having the "lines" issue should just send theirs back. After these tests, I think it is safe to say that you shouldn't experience any lines no matter what.