Get a stress test program like MSI Kombustor and run it for a few minutes. It will show a furry object on the screen which puts a lot of stress on your GPU. If you see any artifacts appearing (white spots, different colored lines or geometric shapes or anything else that is not supposed to be on the screen) then you have pushed the card too far. Keep in mind that these artifacts don't last long, only for a fraction of a second so you have to pay attention during the process.
Also get a program that monitors your GPU temperature. I wouldn't like my GPU to get to 80 Celsius, although the melting point is far above that. I personally like to keep it to below 70-75 under load C. Although, I am not sure about your particular cards safe temps.
So, do this once and if it is stable at your current overclock (1130 core and 1630 memory) increase the core and memory speeds by 10 MHz (preferrably not both at the same time) and do the test again. If it is still stable, do the test again untill you reach the limit (artifacts, temperature or in some cases a driver crash. Driver crashes are not really harmful as far as I know, since most GPUs have safety features and if a driver crash does occur they will revert back to stock speeds) and then lower the speeds back to your last stable overclock.
If it is already not stable at your current overclock, I suggest lowering it to stock speeds and gradually overclocking it again.