i'll share my experience.. using the F16 as a guage.. at 300mm.. it only filled up my entire AF-point square.
with the A380.. 300mm enough to fill up the whole frame just nicely when it is doing the approach.
Good luck!
My advice. get the longest lens you can lay your hands on, and the maximum x TC so shoot the fighter down.
Look for donchua's photos, those were taken at 500mm.. i think he still needs to crop a bit. i'm not sure if he did.