To answer your question: yes. 60 Hz = 60 FPS. Thus, anything over 60 FPS is wasted.
That said, the 5870 isn't necessarily pointless. Keep in mind that as you increase detail and/or resolution (size doesn't matter), FPS will drop. And you should only care about the minimum FPS, as that's the lowest it will drop to. Also, games will get more advanced, meaning the 5870 may begin to use a lot of the power that was previously wasted on older games.