Pentax K10D vs Nikon D300 vs Nikon D90: High ISO Image Noise Performance – Jeff Kott:
I have a Pentax K10D and six limited lenses. I also have a D300 and recently bought a D90 to get similar image quality as the D300 in a more compact package.
I find in going back and forth between the K10D and the D300/D90, that I really appreciate the extra DR and lower noise of the Nikons especially at ISO 640 and 800 which I use a lot.
I make a lot of 16″x 24″ prints and find that I can shoot with impunity at ISO 640 or 800 with the Nikons and get acceptable images with a little bit of noise reduction at ISO 1600.
When I print large with the K10D, I need to use noise reduction software even at ISO 400.