Cold,
I was using a Sigma 150 - 500mm lens at 500mm on a Nikon D90 for all shots. Eagle was 1/500 sec. at f/6.3, ISO 200. Heron - 1/250 sec. at f/6.3, ISO 400. Hawks - 1/1000 sec at f/6.3, ISO 400.
All shots were done handheld. The optic stabilization mechanism of the Sigma lens is very good. In computer developement work done with Lightroom 3.3.