Hi Darlene,
You forgot to mention one lens, the new 80-400G. This lens used to have, in the previous version, a very poor AF performance. The new version is AWESOME in every respect, and it will take at least the new version of the 1.4X, of course, with the corresponding loss of speed at acquiring and the "loss of quality" attributed to teleconverters. I would make sure it is the latest version. Prior version was a dud.
We own that lens and if it pretty good all around. If you need to reach further, put your camera in the crop mode, which will place all sensors on your available canvas, featured very convenient for flight.
With all due respect to other brands, I try to avoid third party lenses. The Tamron is not true 600 (unable at 600mm) and not sure you will be comfortable hand-holding it.
The Sigma, almost 4k in rice and if you need to sell it, they don't keep value at all.
The Nikon 300/4, we both had in our previous Nikon times and it is an excellent lens. It is very sharp and reasonable size and works with the 1.4X
For flight, we don't use the VR since at the s/s seeps we like to use, it would not make any difference and it does slow the AF acquisition. This would be my choice if you don't want to go for the 80-400G.
Good luck in whatever you do!!!!
Fabs