I'm looking forward to buying a second 7d as a back up when the price of used falls - my gain.

Hi I have found that at air shows there is a tendency to use a very long lens. This makes your job harder as you are reducing the field of view and that makes tracking a fast moving target all the more difficult. I have found that no more than 300 a useful size keeping the shutter speed high, with a good shot and camera post processing will help produce a printable pic. Tripods and mono pods all restrict your movement too much.