Hmmm.....I shall be following this thread with interest as I'm in exactly the same situation as yourself. I have a 18-200mm, but get frustrated at not being able to do wildlife/sports due to the restrictions of the max focal length. The 18-200 is a great all round lens but really has it's limitations for wildlife/sports.
I've read a few reviews and understand that the 80-400mm is not very sharp at anything over 300mm and as it's only a f4.5, unless you are shooting in very bright conditions, it's not ver effective. Also, have a look at Ken Rockwell's review of this lens
HERE
The April update is very interesting. He says that the 70-300mm VR performs better and unless you will really miss the additional 100mm, I'm not sure paying £1,160 (compared to around £350 for the 70-300) is worth the extra dosh?
Have you considered/looked at the 300mm f4? Going for around £850.[/QUOTE
Thanks for your reply. I am new to photography and just finding my feet. one of my friends loand me his Sigma 100m-300m f4 lens. I did get some nice photos with this although I would have liked them to have been sharper. I don't know wether this is down to me ,the equipment or the distance I was from the subjects. I hope the replies keep coming on this one.