When you OC, if you set the fan speed up high, like 100%, your temps will remain low. With my above over clock, my temps never go above 54c (with good case ventilation). Also, I see a 20ish percent increase in FPS with crysis. With temps around that point, it is not hard on your card. Plus, if you set profiles with hot-keys, then you can just keep the card stock until you reach a point in a game where things start to slow down. Once you get laggy, hit the hot-key get that boost.
What is not worth doing, is pushing the card to the absolute limit. That 1 or 2 FPS gain is not worth it. Just pull it back a bit once you find the stable max speed.