Wow! Those are very impressive
MTFs, across the board. Particularly with the extender ON at wide.. (I'm wondering though if that MTF was accidentally mixed with the extender OFF at wide...).
This lens is one I am keen to see reviews of (& photos from). I doubt I'll ever buy it (though I can afford it, I can't justify about $12k on a single lens - unless I was a professional - ie needing to use it, and making a living from it - which I am not). I'm an ethusiast (and enjoy photography for myself, and sharing my photos with others.
I would love to rent it (but I expect renting it for eg a few days to a week would still be quite a lot!) I need to convince a good local friend to buy one and let me use it... or I could feel kind & generous; buy one myself and lend out to local friends, thus 'justifying' the purchase to myself more... lol
Well... looking forward to some reviews, and more importantly - images from it (I love wildlife photography). Having a zoom from 200mm @ f/4 to 560mm @ f/5.6 with 4 stops IS and USM focus in 1 package is really what I would like - honestly, much moreso than I would like a fast tele prime eg the 400mm f/2.8. (I don't shoot sports, apart from the occasional 'a bit of sports for fun' aspect).
Size and weight are one reason I love my 70-300mm L - it's a truly portable - yet still very high IQ telezoom lens. Of course that lens only goes to 300mm (which is just over half of 560mm). But the 70-300mm L being so portable, it means I'm often able to get closer to 'jittery critters and birds' - than I would be with a huge, tripod mounted lens.
Cheers.... Let the photos roll on!!