John,


if I were you I'd pick the 100-400 over the 300mm. I doubt that for your needs the 300mm is a big advantage over your 200mm. I had the 70-200 and a lot of times 200mm is really too short for wildlife. I doubt that 300mm would give me a big advantage in those shots. The option to go from 100-400 in a sec looks pretty great to me. Also with nature photography I assume you mean: long walks or hikes trough nature and shooting whatever ends up in front of you? Not sitting still waiting for subjects to enter your frame[:P]


In that case the versatility of the zoom is a feature you'll like a lot. You've got a very nice base with the 100 and 200mm. And I assume you've also got something like a 17-55 to do the wideangled shots? A 100-400 would complete your collection I think.


300mm will give you better IQ perhaps, but I don't know about that and I guess the 100-400 gives you good quality as well []


Good luck!


Jan