hey man, good advice but check out this link to a graphics card compare sight, you may know it already.
http://www.hwcompare.com/13296/geforce-gtx-660-vs-geforce-gtx-660-ti/
looks like the Ti version has some definite upgrades but for the price difference, over $100 bucks, i am not sure I would be getting the most upgrade for my dollar!! i think that the 660 w/ metro last light free is a pretty good deal at $209.99. i run an Asus Maximus III Gene ROG board w/ 14gb Corsair Ram and an Intel i5 processor.
i think that if i grab two of the 660's and a 1050watt ultra power supply, i should be good for quite a while!!!
D