OK new improvement !!!
in the above posted pic you can see my OC i.e
core =680 shader = 1700 memory = 450
And i mentioned that it wasn't stable due to
driver ..... I was 100% right HOW??
1> having nvidia 301.42 driver it wasn't stable on those clocks.........
2> i degraded to nvidia 296.10 driver it wasn't stable on those clocks.........
3> i upgraded to nvidia 306.23 driver it wasn't stable on those clocks.........
4> i downgraded to nvidia 275.27
IT WORKED STABLE even removed artifacts
SO try try again plus every new thing isn't better ...................
The above trick might not work for every card ! ! !