Telephoto Lens Choices for Nikon

[elapid]

I am a keen and experienced amateur photographer interested in wildlife photography (mammals and birds). I have a Nikon D300 and, amongst other lenses, a Sigma 70-200mm f2.8 lens. The lens is great, but I find the 200mm can be limiting and have been disappointed with the results using a 2x teleconverter. So I am looking for a longer fast telephoto lens, particularly for a shooting bears and eagles in Alaska and hopefully an African safari. I doubt I can afford the Nikkor 200-400mm f4 lens, but others I had been considering included:

- Nikkor 300mm f4 IF-ED
- Sigma 300mm f2.8 EX APO DG HSM
- Sigma 120-300mm f2.8 EX DG OS APO HSM
- Sigma 150-500mm f5-6.3 APO DG OS HSM

The Sigma 150-500mm lens is the most economical (~$1,000) with the longest lens, but also the slowest. The Sigma 300mm lens is the fastest and also the most expensive (~$3,000). The Sigma 120-300mm lens is also fast and although it is cheaper than it's sister prime lens I find this oddly worrisome (i.e., why is the 300mm lens better than the 120-300mm lens despite both being f2.8 EX HSM?). The Nikkor 300mm lens is relatively fast and also economical (~$1,200).

Any opinions on the above lenses or other recommendations?

Thanks.

[parker1986]

Read the suggestions here, and then take a look at lens reviews.

Lens Reviews
http://kenrockwell.com
http://www.the-digital-picture.com/Reviews/
http://lens-reviews.com/
http://photozone.de/
http://dpreview.com


Info:
http://www.photographytalk.com/compare- ... ying-guide