The 80-400. Often knocked, seldom matched
Yes, the AF is slower on a D70 compare to a D2x/D2H. On an outright AF speed test, the 70-200VR on a D70 will win hands down due to the 70-200 being an AF-S lens rather than the 80-400's body screw driven AF-D specification.
I'm sure Gary will be along shortly to add his part about the 80-400 focus speed.
[edit: while typing the reply, sure enough
]
The AF shortcoming can be overcome by developing good technique and appropriate use of the focus limit switch.
I use my 80-400 for mainly wildlife and nature work, but have used it before in the 105-135mm@ f/5 range for portraiture.
This and
this image are the only two examples I currently have in my gallery (sorry!) of the type of thing I use it for.
To figure out which combo is best for you includes:
* do I need f/2.8?
* Do I want to swap the TC on and off to get the extra range?
* for the cost difference of the 80-400 vs the 70-200+TC, would I be better buying a combo of the 80-400 and say a Sigma 70-200/Nikon 80-200 2.8?
* consider by the time you put a TC on the 70-200, your aperture range will be getting into the 80-400's territory anyway
If you shoot a lot of low light sport, yeah... get the 70-200VR with TC.
If you currently shoot with a 70-300G equivalent and you're looking to upgrade to something that will give seriously good results without breaking the bank too much - 80-400 is your lens.