Every chip is different. So can't say as to how far you'll be able to oc it. Btw if your satisfied with your current gpu performance , there is no reason for you to oc it
If you would like more performance then try oc-ing it using msi afterburner by gng up 20mhz on each time and putting the gpu on stress (furmark) . If your gpu crashes meaning you may have reached your limit. By then try cranking up the core clock/memory clock by 10mhz and soon to 5mhz to find its stable limit. If you would like higher , you could try increasing the voltages to get a better oc

Bear in mind too high voltages/oc may damage your gpu.