@aroy: your post reminded me of this technical article I came across recently. It discusses the performance & limitations of the 70-300 AF non-ED Nikkor that you may find interesting. In particular, the author remarks ... "Its performance is inadequate for 20+ Megapixel bodies, although samples produced using the 16 Megapixel D7000 appear to be of reasonable quality".
Moore's Law and Telephoto Imaging
The article also lists a number of observations on telephoto lens use that are worth reading (Some have already been covered in this thread by others). One is about lens jitter at the telephoto range. High res (20+MP) sensors are less forgiving to this. To compensate, one must not only stop down the lens adequately (f8-f11 at the long end), but also shoot at sufficiently fast shutter speeds (1/1000s or faster), and raise ISO appropriately. The trade-off is accordingly noisier but sharper images. No free lunch
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