Any more experiences to share after a couple of months of playing around with it? I am mostly interested in it's capabilities and usability with birds in flight. So mostly autofocus. Can anyone elaborate on that? A 500/4 is just so damn expensive that I can't see myself buying one the next 5 years or more, but I do want to have a longer focal length available. And since the 300/4 with a 1.4x extender has somewhat disappointed me in the autofocus for birds in flight department, this could be a nice addition to my arsenal.
Cameras: Canon EOS 7D, Canon EOS 40D
Lenses: Canon EF 17-40/4 L USM, Canon EF 24-105/4 L IS USM, Canon EF 70-200/2.8 L USM, Tamron SP 150-600/5-6.3 Di VC USD, Canon Extender 1.4x II
Want list: Canon EOS 5D Mark III, Tamron SP 90/2.8 VC USD Macro, Canon EF 500/4 L IS USM, Canon Extender 2.0x III