Here are the official power requirements for the ATI Radeon HD 5850 and HD 5870 video cards.
ATI Radeon™ HD5850 System Requirements:
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard
500 Watt or greater power supply with two 75 watt, 6-pin, PCI Express® power connectors.
600 Watt or greater power supply with four 75 watt, 6-pin, PCI Express® power connectors for ATI CrossFireX™ technology in dual mode.
ATI Radeon™ HD5870 System Requirements:
PCI Express® based PC is required with one X16 lane graphics slot available on the motherboard.
500 Watt or greater power supply with two, 75 watt, 6-pin, PCI Express® power connectors.
600 Watt or greater power supply with four, 75 watt, 6-pin, PCI Express® connectors for ATI CrossFireX™ technology in dual mode.
The power supply recommendations are for an entire pc system.
Corsair and Seasonic are two of the brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. One example would be the Antec Earthwatts series which is a major improvement over Antec’s older psu’s like the Basiq models.
You'll need a case that is long enough from front to back to accomodate the 5850. Luckily the 5850 is only 9.5 inches (241mm) long.
You'll need a case that is 8 inches (204mm) wide to accomodate the Hyper 212
No problem! The Lian Li / Dragon Lord comes in 7 different configurations:
http://www.lancoolpc.com/en/product/product04.php?cl_index=1&sc_index=25&ss_index=62
Need more bling? Here ya go:
http://www.lancoolpc.com/en/product/product06.php?pr_index=35&cl_index=1&sc_index=25&ss_index=62