300 f2.8 IS L II plus 2x Mk.III better than 100-400 f4.5/5.6 IS L?

Wait, wait, wait... You are talking about your decision to use the term "for the first time" for the 200-400/4, rather than for the 120-300/2.8 Sigma, right? This wasn't about choosing between the Canon and the Sigma and pre-ordering the 200-400/4, right? Because if it was, you would be my new best friend!

All joking aside, I think you're right that it will be an interesting discussion. Maybe it will motivate people to discuss actual, practical use rather than theoretical optical advantages. (Yes, yes... I know that is asking a lot of the people around here. )