Hello all, Has anyone used both the 300mm f2.8 afs and the 600mm f5.6 (or f4)?? Need your wisdom. I like to shoot wildlife and birding and realized that my 70-300vr isnt cutting it as far as sharpness goes. Its actually great at 300mm, but a review of flickr's pics rendered from 300mm f2.8 is enlightening. So I have already considered the pros and cons of having, or not having, AF and VR etc. putting those concerns aside, can anyone comment on the sharpness and IQ of: 600mm f5.6 ais, older manual focus lens.. how does the IQ sharpness compare to 300mm f2.8 (manual), 300mm f2.8 afs(nonvr), 300mm afs vr1, or 300mm afs vr2? From what I have read, (and visually reviewed on Flickr), the newer afs lenses, in general, have better IQ than the older ais lenses. just looking at flickr at the 600mm f5.6 (or 600mm f4) examples, they just don't seem to come close to a 300mm f2.8 variants such as the nonvr, vr1 or 2. so this is an old versus new, 300mm with or without TC, versus 600mm ai or ais manual focus type of question. (caveat...looking to buy a used lens, budget up to 2k) thanks.