arey dont be angry boss...what i meant is its not worth OCing your graphics card to its limit as in gaming, it will not make an unplayable game playable.
Every card is different, you cant tell how much sehwag will score against Srilanka till he actually plays, right?
Each card has its own unique limit, you may have got a golden batch or a crappy one. I would suggest you do it the old way, increment Core clock in steps of 15MHz, test (run a benchmark) and do it till your system is unstable...