Okay, as you have an i7, It'll definately not be a cpu issue.. Overclocking won't help.
This thread sorta wandered from bad gaming to overclocking.
You have not answered the one important question.... what is the gpu temp..... and it doesn't matter your in a haf.
If thre gpu is heating up, you'll get stuttering.
Have you run a 3d vantage? Great way of seeing if its a gpu or cpu issue.