Either the canon 100-400, because your 24-105 is ok for portraits, bokeh is decent.
Or, the 28-300 l, it is a really gOod lens, or so I hear, your covered for air shows, and air shooting, the 300 also helps.
But you may also want that extra reach. The 3.5 aperture good at the wide end will best your 24-105 though. But, if portraits are that important, pick up a 50mm 1.8/1.4 and/or sell the 24-105 for a 400mm 5.6 is. I know the 24-105 is good for walking around, but either way, you may need to compromise.
Other option, canon 70-200 2.8 is ii. get some extenders and a tamron 28-75 in place of the canon 24-105, the 28-75 is a remarkable lens, I borrowed it from a friend, and it is on par withe the canon 24-70 1 in terms of bokeh, but lacks a bit of sharpness.
I'd prefer option 2, for the versatility.