Most of the 6850's are following the reference design and will be about the same heat and noise level.
As for quiet. If Sapphire releases a vapor-x version, then it will be quiet. I have not seen one yet.
Gigabyte, Asus and Sapphire have there own cooling designs that should be quieter then stock.
There are not many reviews comparing this yet unfortunately. In the 5770 days, the sapphire one was about as quiet as they got with the vapor-x ones.