my gpu, a hd 5870, is from 2009. i have 8gb ram and an i7 2600k. i can play almost everything on high or ultra in 1080p if i want to be over 40fps. battlefield 3 on ultra with only 2x aa and 16x anisotropic filtering and i have i believe 40-45fps (but don't remember exactly). so, maybe for 60fps i have to go little bit down with the specs but i can still run every pc game with more fps and high settings than the console counterpart. i would say it will be enough for 2 more years to play at least most games in high or middle settings to play above 40fps. if i would go down to 720p which is the maximum for most console games atm, i could run everything much much faster than on console with high or ultra settings.
there are few settings for pc games which kill almost every gpu like ubersampling in the witcher 2 (thats like you play the game in double the resolution you really play). i play the witcher 2 without that but everything else on high is fine to have more than 50fps most of the time. maybe sometimes below that not sure.
maybe this will help you for your question.