Very good points!!
Now I'm confused again.
But you've gone from a 1.6 crop to a 1.3 crop so that you can use a 1.4x TC! Not much in it is there? :?
But as my main use is landscape and portrait rather than wildlife/action I think the 5D probably still has the lead for me.
Also I'm really not one of those people who thinks that the most important thing about a lens is how sharp it is. Other factors weigh more heavily with me as long as it reaches a level of "very good" - I don't need it to be the very best.