I had a go at trying to catch a real sharp image of a high altitude aircraft and this was the result.
image hosting tinypics
According to tracking software it was at 36,000 feet. I used my 500mm for this photo.
For me it is not as sharp as I would like so I am thinking of using the 800mm for added sharpness.
Thank you or your replies. I will look into both the book and the courses. Both of them will keep me going for a while.