Matt Cox , Nov 18, 2000; 01:21 p.m.
Although I have not used the new 300f4 AF-S, I have used other AFS lenses (500, 80-200) and have been testing the new 80-400. Assuming the 300f4 focuses as fast as other AFS lenses (pretty safe assumption), there is really no comparison for birds in flight -- get the 300. On the 80-400, the performance of the VR feature is outstanding, as is the image quality and flexibility of the zoom, but the autofocus is way too slow if the primary use is birds in flight (by my simple tests, AF-S lenses focus twice as fast as the new 80-400). If you want a lens for more than just birds in flight, than the answer may be different.
Matt Cox Parker, CO