Noise reduction in 5Dmk3
Can I turn off Noise reduction in Low Iso to get better detail?
My questoin was concerning jpeg
sorry to say that turning off NR for JPEGs doesn't sound like a good idea. the reason is that JPEG produces noises of its own while coding, it produces more noises if there are more noises in the original image, and this is a distructive process that won't be recoved at post.
also it's not a good idea to push a JPEG image more than 1 EV because there are only 255 levels of coding. there is not much in the sadow because the format doesn't allow smooth tones there.