Just across these posts . The image quality at ISO 6400 is simply amazing. It’s almost good as Nikon D7000′s ISO performance , IMO.
Check the images here: link 1 , link 2 , link 3 , link 4
ISO 51200 ( wow ) : link
another sets : ISO 12800 , ISO 25600 , ISO 51200
iso 800 , iso 1600 and iso 3200