It looks like the HD5830 may have a similar power consumption to an HD4830:
http://www.nvnews.net/vbulletin/showthread.php?t=142654
Here is the actual web-page for the cooler:
http://www.silenx.com/ixtremaproheat...?sku=ixg-80ha2
Looks like an HD5890 is also in the works.