I been using my 6D for a couple of weeks and I'm very pleased with it's low noise level. My previous camera was a T2i/D550 and I always process the photos with Nik Software Define to reduce noise after shooting in RAW and converting to JPEG with 0 noise reduction and 0 sharpening in DPP. With the 6D I usually shoot at ISO 1600 and often skip Define altogether. Here's an example of a 1:1 crop of a bird shot with no noise reduction. The second shot has some resampleing to create a computer size image and with the background process with Define but not the bird.
|Bianca Buitendag-7809 by vbuhay|
|Sunrise in Paradise by OB Foto|
from Booby Prize
|The Battle for the Lead by Photo Pete|
from Bicycle sports
|Cecelia's Eyes by Madeleine Hart|
from - Jenny from the Block - (Colors that pop + A white Border)