I don't have that fancy 100-400, I do however have the fancy 70-200. Serves me quite well for the most part. This lens is stupid sharp. At least to my untrained eye. Aside from birds, I usually have plenty of reach. Sadly, the only real "wildlife" around here is squirrels and ugly ass canadian geese. With the occasional mallard duck.
That's some really nice subject/background separation, and rich color. Nice work!