Hi Bill,
Your choice among the telephoto options really depends on your needs.
How often do you have the need for something longer than 300mm, and
how much longer, and under what lighting conditions?
Since 3 out of the 4 options you mentioned call for a 2x AF tele-
converter, you might just buy that and see how it works. My father
had a Tamron 2x converter that he used with the Nikon 70-210 f/4-5.6
and not only were the results acceptable for him, but the combination
actually autofocused with his N6006. Now you may be more demanding
than my father in terms of sharpness and may have a fondness for slow
slide films which would make the speed unacceptable, so look at your
needs carefully. Also, if you go with a combination like the 70-300
and a 2x and have hopes that it might autofocus, make sure you try out
the converter with your lens and body -- not all combinations work.
I'm not saying that this is the right choice for you, but my point is
that the combined opinions of this august group will never be as good
as your own examination of your needs and some trial and error.
Oh, and if you're looking for other options, you might consider the
Tokina 400 f/5.6. It's reputedly a very good lens, is not very exp-
ensive, and is propbably sharper than a shorter prime or zoom with a
teleconverter.
Good luck
Dennis
