Nice selection of garden birds. I too have a D300s but haven't experienced any issues with noise above ISO 600. I think in this situation I would have used a higher shutter speed such as 1250 or 1600 and increased my DoF to 5.6. This should give you more detail in the feathers and blurred the background more. Did you use a tripod?
I think your images of both the sparrow (3) and starling (1) are best as they show catchlight in the eyes. Image 2 by contrast doesn't have this catchlight and therefore the dove looks a little flat. Thanks for the software tip. Have you seen the Blue Crane video for the D300s? There are lots of tips for making the best use of the camera on it. Thank you for sharing.