2x GTX 660Ti's is more than enough to max out any current games at that resolution. And if you think u need to get another, a recent Tom's Hardware article stated how 3 660Ti's is better than 2 GTX 680's.
Where's the link to that article?
Update --- Found it:http://www.tomshardware.com/reviews/geforce-gtx-680-geforce-gtx-660-ti-sli,3429-5.html
Id still go with 2x670s, because 3 670s in the future is still better than 3 660s. If I were going to halt all upgrades on the system, I'd go for the three 660 ti now.
But still, a single 670 would max out everything at that resolution.