if i may give my humble opinion about noise reduction for sony alpha 900 (since i am still a beginner and need to learn more about photography):
i used to shot using iso 200-400 (with alpha 900), and for doing portrait shot i also used to bring sony flash (HVL 58 AM & HVL 20 AM), and the result is clear & good + i am satisfied with it (for my self, i find all results are low amount of noise). i have to say that sony alpha 900 (ofcourse with its own plus-minus aspects) is a great camera, that make me possible to learn + explore many things in photography with very user friendly way/ technology. i am almost 99% satisfied with the image quality result. the thing that i've learned is that i have to make the good setting for camera (iso, exposure, wb, flash, creative style, etc) in order to get the better result. so i have to pay more attention to set the camera. The mood and creativity of photo is also more important for me rather than thinking to much about noise at the photo itself. have a nice & happy shooting time for you all, cheer ;p