The 100-400 is a fine lens and produces outstanding results. I've taken literally thousands of photos with that lens, on my 7D and also on my 5Diii. One bit of advice: avoid shooting wide open if possible. It's ok at f4-5.6 but it really shines at f7.1 and f8.
I was hoping to obtain at least this sharpness with my 100-400L and the to be purchased 70D.