I know nothing and am not too bright so be kind.Why would you say that? It will be about the same size as the existing 200-400, with a longer reach. Frankly, I'm not sure why they would produce this lens. How is it any different than buying a 200-400 and a 1.4x III? With these two items you'll have almost identical ranges of 280-560mm f/5.6 and 400-800mm f/8, with the added benefit of using it natively without the TC as a 200-400mm f/4. Granted, Canon could optimize the lens better to have slightly better IQ without double-stacked 1.4x TCs, but does that really justify this lens? The front element will be slightly larger (107mm vs. 100mm, theoretical), the rumored lens will likely be longer and weigh slightly more, so no size/weigh advantage exists. And I'd imagine with its longer reach it will be more expensive than the current offering + the cost of a 1.4x TC. Anyone have any other ideas about this rumored lens' raison d'être?
I see the 200-400 as part of the 24-70/70-200 f/2.8 L II line of lenses.
I expect the 300-600 will be part fo the 24-70 f/4 L , 70-300 f/4-5.6 L line of lenses.
Relative to the 200-400 I'd expect to sacrifice some image and build quality but in return get significant $ in my pocket and a relatively lighter lens. I'm going to set my flag at the $8000 price point. I would not be surprised if it was even lower.
Like I said, I know nothing and am not too bright so be kind.