I do fear my 100-400L might be worn out from the use I've given it over the years. The push-pull mechanism isn't as smooth as it used to be, so a long(er) replacement isn't out of the question. No push-pull remains a disappointment to me but not unexpected.
Since the 600mm class lenses have also been bought up, to me the Tamron is not an option with its backward zoom ring. That leaves the two new Sigma lenses. I already have the 120-300 f/2.8 (to get 600 with a x2) and the '600 S will be similar in weight. A bit too much for regular use on the move. On the other hand, I'm not sure how good the C will be.
Or maybe I should just get another 100-400L before they stop making them
Even bring back the 35-350!