This is a great lens for wildlife photography, it some ways better than the 300mm f/2.8 considering it is a lot lighter and about a fifth of the price
Here is a few shots I have taken with this 400mm f/5.6 lens – http://www.flickr.com/photos/darragh/tags/400mm/
The only lenses that will maintain autofocus with a tele-extender on 30/40/50D bodies are f/2.8 lenses and the 300mm f/2.8 lens is the closest in terms of focal length but will cost €5k from Conns.
Steve keeps all his gear in prefect condition, always kept clean and well stored. I have bought stuff from Steve before.