In my own use I condider the 2.0III to be superior to the 1.7 in every regard except that with the 2.0 the autofocus is intermittent since it starts at f/8. I guess a couple of the new cameras allow you to use a few AF points at f/8.
I use all three Nikon tcs on my 200-400, 500, 600 lenses.
Thanks Jim. I was really disheartened to learn that the AF feature doesn't work with the 1.7 and 2.0. You'd think that Nikor would have figured this out seeing as their customers who are selling kidneys and remortgaging houses to buy the 500 or 600mm. I can only suspect that the TC's are focused for use on the big lens'
Anywho... I appreciate the insight. I was leaning towards the 2.0 but had heard that it is a bit softer compared to the 1.7.
It's not that the autofocus doesn't work, it's that the autofocus is unreliable.
Being only a stop and a half loss of light compared to two stops for the 2.0, the 1.7 exhibits much better autofocus capability in my opinion. I don't hesitate to use the 1.7 on a regular basis, accepting that the autofocus will be less than perfect. The 2.0 I reserve for perfectly sunny days. If I were only getting one it would be the 1.7.
Rick, if you are going to stick with the D7000 or by switching to fx you mean moving to a D3/D3s/D700 then the 1.7x will work within its AF limitations. So will the 2.0x provided you have good light, but less so than the 1.7x. The 2.0E III will give better optical results, as stated by other posters. If you move to the D600/800/D4 then things change. The center sensors AF to f/8. My 500 f/4 has no problems with the 1.7x on my D600 and I am about to order the 2.0x. On my D300/D7000 the 1.7x either hunts, or fails, under less than ideal lighting conditions with both the 500mm and 300mm f/4. For the new D600/4/800 cameras I would be very tempted to bypass the 1.7x in favor of the 2.0.
I get better sharpness by avoiding the 2.0 teleconverter in favor of the 1.4 and occasionally 1.7. The new 2.0 is very good for a 2.0 - it's nearly the same in image quality as the 1.7. But the loss of light is a killer.
When you look at how sharp images can be with the bare lens, there is a significant drop off in quality with the 2.0. More importantly, the minimum aperture of f/8 and better results stopped down to f/11 or beyond means you need exceptionally good light with the 2.0.
I find the 1.4 teleconverter is my choice over the 1.7 and 2.0. Image quality and shutter speed are typically more important than a little more reach.