K-5 can produce fantastic low noise images. Got to agree with @Anvh that slight overexposure gives better results ito noise performance. I've been completely blown away by the high ISO performance, and it has breathed new life into my slow long lens, namely 170-500. I can now shoot TvAv, and let the ISO range go up to ISO6400. Previously with the K200d (probably similar ISO performance to K-7) I was getting unacceptable results at anything above ISO400.
But don't know how to contrast against 5d MkII, so perhaps example is best to demonstrate potential. This is ISO6400 1/250s f/9.5 450mm. Straight out of camera, but with resize and quality drop for posting.
Last edited by KevinR; 12-28-2011 at 01:03 PM.