We have one of the lenses you mention, the 70-300DO IS, and it's a very good lens.
Many of the critics fail to realise that image quality isn't everything, although there is
nothing wrong with it's IQ. Where the lens shines is it's combination of fast autofocus,
excellent stabilization, low weight, good balance and handling. We use it as a general
travel and walk-around lens, when we don't want to lug around the heavy metal.
The problem with all the lenses you mention is that they are all too short for birds,
and even most animals. The 70-300 is perfect for Elephants, Giraffes, and big
birds if you can get really close. We also got good photos of Lions and Leopard, but
undoubtably the longer lenses are better. Heres one of my wifes Leopard photos with
the 70-300DO:
http://farm3.static.flickr.com/2067/217 ... 0a16_m.jpg
and this one is also using the 70-300DO (but its not from South Africa so only look at
it for research purposes!). It does show that even birds in flight are possible.
http://www.flickr.com/photos/22594688@N08/2407266357/
/Neil