Sapphire HD 5830 runs at reference clocks – 800MHz for the core and 1000MHz for the memory. We easily pushed the card to 875MHz and the memory to 1200MHz (4800MHz effectively), which is the maximum allowed by ATI’s Overdrive.
As far as consumption goes, the card will consume more than HD 5850 in 3D, but less when in idle.
The thermals are great, as you can see from the picture below, and we really liked the quiet cooler. In fact, the cooler is inaudible when the card is in idle mode and gets only a bit louder than that during more intensive tasks.