Running 2x HD 5850 at 320 mhash/s each (-v -w128 -f30 options, cpu clock: 850mhz, mem clock: 335 mhz) and another rig with 1x HD 6950 at 345 mhash/s (-v -w128, cpu clock: 900 mhz, mem clock: 530 mhz). Seem pretty stable but I still want to get temperature a bit lower (currently about 75-78°C)