Upgrade from 40D to 60D or 7D for nature photography?

Hi,

I have a 40D and am going to Colorado Springs and Banff next May. I am tempted to buy a second body so I can have my 100-400 IS Zoom at the ready while taking in the scenery with the 24-70L. Wildlife - birds and animals and all nature shots are my particular passion.

I've been following the thread about the 60D being a bit soft - in fact I thought that from the sample shots in the review and I would hate it if my shots are soft or lacking in colour saturation.

So the question is....if price is affordable, am I better with the 7D? One advantage of the crop camera is that my zoom lens gives me more zoom. So if I put the zoom on the 40D, and the 24-70L on the 7D, would I be getting the best of both worlds? It would also give me true 24mm and that sounds pretty good, too.

Is the 7D a lot better than the 60D? Conversely, if I buy the 60D, then that should be even faster with the 100-400 IS.

Comments about the 60D being downgraded to plastic? Is the 60D still better than the 40D or closer to the entry level models? (As a comparison in my mind).
There are rumours about a 70D. I could wait until next April.

Is it the camera that gives soft shots, or the lenses and of course the operator??? Would there be a difference between the 40D, 60D and/or 7D with the very sharp lenses I will be using?
Many thanks,
--
Glenys