For sure. Overclocking the Asus 5850's is easy. Just uninstall Asus's Smart Doctor, and install MSI Afterburner. Then drag the slider, save the profile and enjoy
I run 900/1000 daily on mine with the stock heat sink. During games temps rise to about 60C and the fps skyrockets
But I mainly use my GPU's for BOINC (similar to f@h) and under 100% load while crunching, the temps hover around 75C for 24/7.