You get a lower amount of cuda cores with the 660 (non ti). Since you are wanting EVGA looks like the 660 (the non ti version). At the price point the ti version is more expensive then it needs to be because the 7950 is at the same price point and it performs better.
Now if you wanted something better then the gtx660 you would notice a larger jump with the 670 which is very close to a 680.
660 Ti performs better when overclocked... I'd just go for the GTX 660 (Non-Ti). It costs a LOT Less, and I noticed the Ti had a lower Dip in FPS and in MAX FPS, it had a 1 frame advantage. Imo, the 660 is better than the Ti version, Nvidia messed up with this.
Would you still recommend the non ti 660 and pass on the savings, or should I wait and save for a GTX 670.
Every two years I plant to upgrade the card.
Yes! 660 is enough! I've noticed that approximately every 2 years the benchmarks show the the x60 cards are the same performance the the previous year x80 card. Example, the GTX 660 Ti performs almost on par with a GTX 580.