I use converted Canon FD 300/2.8 and 400/2.8 lenses on my EOS 5D classic.
Cause I have the EE-S screen in, I am not sure, but I suppose for f/2.8 and slower lenses the EE-S screen is not so much help. For fast lenses faster f/2.8 EE-S is more useful, and for f/1.2-1.4 lenses it is extreme helpful. The same for the EG-S as well.
I do sometimes take images of moving objects with those lenses. It is not easy, but at least your focus is not bewildert from tree branches in the foreground and such.
EOS 5D + Canon EOS FD 400mm f/2.8L
I love the Nikon lenses I have, but bought the big Canon tele lenses, they are cheaper than the Nikkor counterparts - at least the 400/2.8 and 800/5.6.
For the manual 300/2.8 Nikon and Canon seems on ~same price level.