Brad, you said "I'd bet even money that the 100-500 is at 6.3 @ 400mm" I said "I'll take the bet," and gave some of my presumptions and technical speculations below as to why (you call these "assertions" to justify what others describe as a snotty response). You call these assertions to justify "calling me out." Is this a playground bully battles I've stumbled into? Are there alpha nerds I'm threatening with technical speculations? Here what I wrote that seems to have triggered you - emphasis added:
Agreed. Not necessarily 5.6 at 400, but I'll wager that when you have an established and successful multi-generation 100-400mm design that gives 5.6 at 400, all the designer basically (simplistically) needs to do it to make a telescoping tube a little longer and pull the objective lens a little father forward to get to 500mm. Honestly, if we took apart a 100-400 and just held the front element a little father forward, it would presumably image as a 500.
Granted, lens design has subtleties, and there would presumably be issues introduced (possible mechanical getting that telescope distance - I'd cringe at a three-part telescope). But it's hard to imagine that the change would require reducing the aperture at 400mm. That's the last solution the designer would be allowed by the boss to revert to.
If seeing my actual words causes you to reassess anything you posted, please let me know.