To overclock today we are using the latest V4.0.0 of MSI's Afterburner based on the excellent Rivatuner.
We were able to push the core to 1,453 mhz, with the Turbo Speed set at 1,554mhz. This translates into a 18.3% overclock which is very healthy indeed. Every card will exhibit slightly different overclocking capabilities, so there will be some variance between them.
Great card!