OCing a GPU isn't worth the risk IMO, the outcome will not give you much more power and you potentially risk damaging your card in the long run. Also as everyone has pointed out, your card will just run hotter, not good for the upcoming Summer months, could knock some life off of your card, well unless you've got some decent water cooling.
If you still are really intent on OCing your GPU, make sure you read through countless top notch forums and posts from hundreds of people who have done it with that card, you have to be 100% accurate with what you're doing and what your aims are before you do something like this. I really don't see the point in your GPU being overclocked though, it's a good card already.