06-12-2020 05:26 PM
"There are times when f2.8 vs f4 does make an important difference:"
Absolutely and exactly why you buy the lens that fits your requirements and needs. The main and only most important consideration.
06-12-2020 05:33 PM
"That said, have you seen what they do with your luggage?"
I worked for and traveled for a large maybe the largest photography company there is. What I have tried to advise you is from that experience. I know one of my co-workers that lost all their gear on one trip.
Canon makes these kinds of lenses especially for that kind of work. Canon is well aware of baggage handlers and shippers believe me.
I have seen guys throw their big lens in the case and not from an inch or two but feet away. I have seen guys sit on their lenses and more. The average Joe just does not need that kind of build.
06-12-2020 05:37 PM
"Depending upon the body, a f2.8 or faster lens will activate dual cross point sensors in the AF array providing for the highest AF performance from that lens/body combination."
I don't think f/2.8 is set in stone. Before I gave it away to my son, I think my EF 24-105mm f/4L IS USM would enable, let's call it wide aperture mode, with my 6D. The firmware seems to make exceptions for many of the f/4L lenses.
Note, this does not mean all f/4 lenses, just the Canon L glass f/4 lenses. I guess I need to look it up to confirm if the 300 f/4L activates the f/2.8 wide aperture mode, but I would strongly suspect that it would.
Just like teleconverters are designed to work primarily with telephoto primes, the firmware allows exceptions with many L glass telephoto zooms, like the 70-200s. Activating "wide aperture mode" is permitted in firmware with many f/4L lenses.