According to Peter Braczko's guilde: Complete Nikon System. There are two different AI-S versions of the 300mm/f2.8. The first AI-S version differs from the older AI because AI-S version 1 has an additional clear, protection filter in front. AI-S version 2 can focus closer down to 9.8 feet/3 meters. More info on Roland Vink's web site: NikonNikon 300mm f/4D AF-S vs Nikon 80-400mm f/4.5-5.6G VR Conclusion Although both lenses seem to perform well at 300mm and 420mm focal lengths when stopped down to f/8, as demonstrated in the above charts, I would still recommend the Nikon 300mm f/4D over the 80-400mm lens for two main reasons – autofocus performance/accuracy and better reach.
The Nikon 120-300mm is a 50% longer focal-length version of an 80-200mm f/2.8 lens, with the same fast f/2.8 maximum aperture. Making the focal lengths "just" 50% longer with the same maximum aperture require an inordinate amount of engineering, materials, size, weight and expense.
Nikon AF-S Nikkor 300mm f/2.8G ED-IF VR Nikon AF-S Nikkor 300mm f/4D ED-IF Nikon AF-S Nikkor 35mm f/1.4G Nikon AF-S Nikkor 35mm F1.8G ED Nikon AF-S Nikkor 400mm f/2.8D ED-IF II Nikon AF-S Nikkor 400mm f/2.8E FL ED VR Nikon AF-S Nikkor 400mm f/2.8G ED VR II