Hi Leon
Just a few ramblings from me Leon, as I have no experience with this lens.
I have seen a few photos of birds (static – on branches, etc.) taken with this (Sports) lens (on various photography forums) and they looked very impressive. The detail in the feathers was excellent and the sharpness across the frame was also excellent without appearing over-sharpened or pushed too hard.
I’m not too sure how much variation there is in image quality between various copies of this lens and what can be adjusted in terms of Canon’s micro-adjustment if a lens either back focuses or front focuses.
I also suspect that the user has a significant role to play in terms of shooting technique. Some folks can shoot at insanely low shutter speeds and still produce sharp images whereas others “jab” at the shutter release and produce varying degrees of camera shake.
I have seen these lenses in the shops and they do look big and heavy!
Cheers
Dennis