Upload & Sell: On
the AF on the 7D is more advanced in terms on in flight shots with point expansions and what not many will draw on this. For the 70D I have enjoyed it thoroughly for bird photography. High ISO (1600-3200) has been fine for my likings (I could not stand the 7D at ISO 800). For in flight photography, I did really well with the 7D . . . but I also did quite well with the 5D Mark II which has a poor AF system in comparison. The 70D Will give you better AF in live view, but about the same AF when focusing through the viewfinder IMO. Many will contradict this, but these are also people who have not spent time with a 70D.
If AF is a main concern, you may also consider the 1D Mark III used for about the same price. It's a work horse camera, and I use mine a bit as of lately, even with the 70D.
Background for that - I did shoot a 7D for almost 2 years before moving to a 5D mark II, then used the 7D as a backup. I replaced it with a 1D Mark III, and still use it. I picked up a 70D for fun, and have also used it for bird photography with great results, even in harsh conditions.
70D, 500mm F4 IS L with 1.4x EF II TC. F7.1, ISO 2000, Exp 1/25