are you kidding?
legit reviews: +2w difference
tom's: +8w at idle, -10w at load
fudzilla: -2w at idle, +10w at load
anandtech: -1w at idle, +17w at load
again, the power consumption is not good (bordering on bad), but it isn't absolutely terrible. The 5850 itself was extremely power efficient in the first place as well. If anything, it should be compared against the GTX 275 and HD 4890, the cards it will be competing against.
as for performance, it is around the same as the release of the 5770. A bit under the previous holder at that pricepoint. Just the 5830 is too expensive.
Edit: Another note about the power consumption is that some reviews are giving it 260W at load, and others are giving it around 350W at load... which is actually something I didn't notice earlier.