MSI have their own Afterburner software for overclocking and we used the latest beta version which supports this card directly, with several voltage settings.
We found that the core reached a limit around 1,240mhz, regardless of the software or voltage tweaks. We actually achieved the same results with a slightly different version of Afterburner which opened up a Power Limit percentage reading (shown below).
Both core and memory clocks could be increased by just under 13 percent, good results.