I went out to a local park the other day with my 5D3 and 70-200 f2.8L IS MkII. I was looking for squirrels and birds to shoot and I did get some great shots close up, but anything over about 15-20 feet I found I wanted longer. I put my MkIII 2x converter on and found that was so much better but the IQ took a bit of a hit. If it was me I'd keep the 100-400 for wildlife shots, the 70-200 is woefully short for most things.