Overclocking will pretty much always give you better performance, but that card is so old I'm not sure you'd notice. You may get a few more FPS out of games, but I really doubt it would be enough to crank up the detail any more than it already is.
With hardware that far out of date, there's really not much you can do.
overclocking has very little impact on the GPU temperature when the card remains at the stock voltage (so overclocking on a videocard on a desktop PC is safe and recommended (the amd/ ati drivers will even do it for you (though not as good as if you were to manually do it)
And as long as temperatures are not near the factory limits, overclocking is safe, just make sure your card dont cross 80°C, (70 is safest, 75 is managable and above 80 is red zone in mid to low range cards, but in high end some of them go to 100+ still safe for them as they are designed to run safely even on that hot)
In short if 6-7% is not significant for you and there is no reason to Overclock it but at the same time there is no reason not to Overclock it either as long as its in safe Temperature.