I was gonna +1 that until the 'huge increase' bit... you started by saying not any noticeable performance increase? First statement is correct - you're looking at an average gain of 10% tops. So moving from 30fps up to 33fps. I'd stick with the GTX660.
I actually meant to say slight, and I didnt even realize I said that until you pointed it out, as I'm in skype with some friends and there talking to me about other cards and components I lost track of what I was going to say. Sorry man! And I was referring to the performance increase of the "NON" Ti version over the Ti.