I run a GTX 560 card and only have a core2duo processor and I am extremely happy with the game. I think with you having an i7 that is above the recommended specs a 560 would more than serve you well. I can run most of the settings on high or highest with no problem.

As stated by other posters, it all has to do with what you want out of your system. If you mostly plan on playing this game only as I do then I would say there is no need for the 600 series cards since the 2.0 engin is supposed to be easier to run than current game. BUT, if you play a lot of other PC games then planning for the future with a 600 series may save you money in the long run.