Afaik, the Amp editions used a reference pcb that already had a halfway decent OC applied, just using a different heatsink/shroud. There really wasn't much room for improvement as they were already running close to maxed out with what the board could handle. As said, wasn't hard to get bad thermals as a result unless the gpu saw very good intake airflow.
Strongly caution any further OC, especially if the card is aged as the chances of breakdown multiply drastically with components that already have seen next to abuse levels of heat and voltages.