You may try few things to improvement:
1. CPL
2. Knowing where is your focus point.(some software dose that)
3. Try use F8-5.6(better in-focus range), ISO1600-3200, 1/2500
4. Mount your gun on tripod vs sidekick(Kirk) or Gimbal (Wimberley) then dynamic AF focus mode pin/lock the object.
Personally, I believe Nikon(d3/d300/d700) 15- cross-sensors is much better than Canon 9-in-line-sensors.
Shooting air show is not cheap (I learned it in the hard way). My setups are Nikon D700/D3, 200-400mmVR, 70-200mmVR, KingCobra head on Gitzo 3 serial tripod. I am very happy with it so for.