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.
|Fangorn Forest by cand1d|
|Yosemite Falls with Moonbow by Jonathan Shapiro|
from Best Landscape of the Week 4