I have a Sapphire Radeon HD 7850 2GB model that I have overclocked... It still runs plenty cool, so there shouldn't be any issues with longevity.
Core: 860 1050
Mem: 1200 1450
I have hit the end of the sliders for MSI Afterburner. Going to have to find a way to raise the limit as I dont think that I have hit the end of what this card is capable of.