I think you’ll need the larger Gitzo bag to fit the 600mm f/4, however regarding on whether or not the larger bag would be allowed on a plane as a carry on I’d suggest checking your airline website on what they allow as my understanding is it depends on the over all measurements of the bag & it’s weight, not it’s volume.
The interior dimensions on B&H seem like it “should “ fit a 600 F4 (Sony GM or Nikon Z 600 TC) unattached, but the camera insert is removable so it’s unclear if the interior dimensions account for the insert padding or not. That’s why I was hoping someone had some hands on experience with it. I guess the lack of photographers using it may be a sign?
That’s helpful, thanks! Because B&H says the 45L internal height is 541mm, so that tells me the internal dimensions are without the insert. Therefore the insert on the 30L is probably not big enough for a 600 F4. That settles it.
As for air travel, many years ago the FAA declared that professional photographers can have an additional camera bag with them that does not need to be checked regardless of airline policy. There are two issues with this. First, how do you prove you are a professional (and what if you are not)? Second, how many average airline employees are actually familiar with this ruling (and if not, how many will take the time to look into it, especially while a plane is boarding)?