I spent some time the other day testing the 7D2 with the 100-400 II for BIF, and came away fairly impressed. It's not a lightning-fast AF combination (at least in the challenging conditions I was shooting in), but a good number of the frames were sharp. The challenges included a varied BG, mixed sun and shade, and birds that were quite close to me (and thus moved across my FOV quite rapidly). Here's an American Wigeon; I'll include an unprocessed 100% RAW file crop in my next post. I used Case 4 and top/bottom/left/right focus point expansion for this shot.
Canon 7D Mark II, 100-400 II @ 300 mm, f/7.1, ISO 800, 1/2500, manual exposure, hand held