Portal 2 stuttering issue

I've got a gtx 780/core i7/windows 7 and all drivers updated

i've found that portal 2 tends to stutter somewhat annoyingly from time to time. turning off multicore rendering helps a little, but if i leave it off when i quit the game, when i start again and try to load the current level again the game hangs. also i haven't tried turning off vysnc, though i hate screen tearing, so i'd rather not

I would enable Vsync with triple buffering, enable multi core rendering, defrag your harddrive/s(not with windows defrag use defraggler or smart defrag), make sure to shut off all apps running in the background too. You could also set portal 2's cpu affinity to your last four threads/cores which will allow the 1st core to run windows and apps without having to run the game as well.