What to replace Kit lenses with?
You have some nice lenses. Never get rid of the 10-22 its a definite keeper the 85 is also nice. I use the 400 5.6 it is tack sharp and the AF is not as bad as others report. I shoot motorcycle racing and at 175mph (250+ FPS) you pan any way. Same with birds I shoot them oppertunistically that is I live a short distance from several rookeries so why not. I used to do nature and landscpe/ architecture. Read the forgotten 400 before you invest in a 100-400. This is still a good lens, however everyone fails to mention both these lenses are very agged. On the other side I see more than enough 100-400's when I am shooting at the rookeries. Again, as all say rent it, check it out. if price is no object the 500 4 ll has the best MTF I have ever seen on a Canon lens. Also consider what else you are likely to shoot. This will help greatly in your decision.
Thanks conofodder. I hadn't looked into the 400prime, but after some research - yes, I think that may be preferable to the 100-400, even without IS. Cheers, DG