HowlinWolf I, like SeaJay, have done a fair bit of research on the internet especially at the nikonians site where a lot of people use both lenses and post many images as to their respective quality. Being just under £4K the 200-400 is obviously superior, being acclaimed as one of Nikon's best ever lenses. Even with TC 1.4 and 1.7, gives tack-sharp images.
The 80-400 is a more modest price, just £1000, but doesn't have silent-wave motor and is not recommended to be used with nikkor TCs, but can with Kenco Pro 300 1.4 TC for Nikon AF-S.
I have the 80-400mm and find it useful but it takes some practicing with and re-evaluating of one's long-lens-technique.
So, all-in-all, if money or time's no object, get the 200-400, but if it is, get the 80-400.
You won't be disappointed with either.
