Hi James,
I believe that the sigma 80-400 should work on the D300 the same as it does
on the D200. I don't have the D300 yet so I can't really confirm that.

These are my thoughts on the Sigma 80-400
Pros
- A good hand held lens for that range to capture quick shots
- OS works great for hand held applications.
- You can force the focus while in autofocus if needed.

Cons
- Not as sharp as I would have liked it to be (my copy)
- Never have liked a variable F stop
- 1.4 extender worked, but only on MF.
- I removed the mounting collar to make it more comfortable to hand hold

Overall I like the lens, but I am still renting different lenses until I find
the one that will work best for me.

This is another image of the Turkeys when they were in the woods.
You can see that they are all looking straight at me. Even the 5th turkey
on the right is looking over the tail feathers of #4. I think that's why it
is so difficult to get good shots of wild turkeys. They must have incredible eye site.





Below is an image taken just after the turkey shots when I switched back to my
Nikon 50-300 ED F4.5 Zoom Lens. (Always has been my favorite lens ) I would
probably remove the grass coming out of the back of the turkey if I decided to
print this image. I never ever add anything to an image, but I don't have a problem
removing something if it is drawing my eye to it.



Below is an image taken with the Sigma 120 - 300 F2.8 with the Sigma 1.4 extender. (on tripod though)
I like the bokeh that the Sigma 120-300 gave me on this lens. I always tend to shoot wide open and always
manually focus on the eyes of my subject to let everything else go out of focus etc. I rarely use autofocus.




My next lens to check out will be the Sigma 100-300mm
Unless I hit the lottery and just go ahead and buy the Nikon 200-400mm

Hope this helps.
I would suggest renting a lens to try it before you purchase it though.
I use www.lensrentals.com
I highly recommend them. quick service and very helpful. you can also reserve a lens ahead etc. which helps when
you are planning a trip in the future etc.

Dale