The weather improved considerably over the last few day, so I went out some more with the 7DII and the 100-400II. I do like the combo. The IS is very good and both IQ and AF speed are as good as the 400 5.6 in my view. No scientific comparisons, just my feeling when shooting with the combo. Adding the 1.4II converter does not take away much of the image quality. It does affect AF speed, of course, but it remains quite fast. Being limited to the centre AF point (+4 assist points) makes BIF a little harder, but with more or less 'busy' backgrounds, that is what I would use anyway. Some shots, all were cropped considerably:
1. Northern Shoveler ( 400mm - 15% of original)
2. Tufted Duck (400mm - 23% of original)
3. Common Whitethroat (560mm - 20% of original))
4. Willow Warbler (560mm - 26% of original))
5. Mediterranean Gull (560mm - 23% of original)