F8 focus with the 40D?
Good point. No it doesn't. I think it won't for earlier bodies (pre-5DIII and pre-70D?) or is limited to a few focus points. Food for thought for those thinking about using it with AF.
For me it never mattered. I always used manual focus (except for people, dogs, and some macros) with or without extenders or extension tubes. Even for bugs-in-flight and birds-in-flight. The 300mm has a wonderfully precise focus ring with just the right amount of travel to make focusing easy. Same with the 500mm f/4L IS (first generation at least).
Have yet to attempt a single BIF with either the 7D2 or 5D4 with AF. Looking forward to it. I'm sure it will increase my success rate.