Games rely more on the dedicated GPU for rendering. Some games are more CPU intensive, granted. I wouldn't call the i7 overkill when it comes to modern demanding games, but the focus really should be more on the GPU, as that may or may not be upgradeable in the future. With the CPU, you could at least go i5 for now and later upgrade to an i7; possibly even an extreme edition down the road.
To answer your initial question: With a 765M - or even a 770M - you should be able to play games on high - ultra settings for another couple of years. 2014 is bound to put the 765M to work, while the 770M should be able to keep up a bit better. Most likely sometime next year you'll be required to turn things down to medium high - high with the 765M to maintain good FPS, while the 770M may be able to run things at high - ultra at slightly better FPS.