I can go with it for at least two years. Currently playing 99.9% of the games in their highest details and 0.1% (Metro 2033) with high details. Say after one year, I need to play some of the games with high setting, some with medium setting and rest of them will be still playable with highest settings.
And making a 30K GPU obsolete is real tough. If you are having a HD 4870X2 or GTX 285 or GTX 295, it can play all today's game with high settings. Even a older HD 4870 can play all the current gen games with decent setting. And it was released more than 2 years back.
So bro, obsolesce will not come suddenly, it will take time.