The 1Dx is not mine,.... yet.. (only tried it with the 24-70 II and 70-200 II) back in june last year, so my experience with it is limited, and the 1D IV I have never tried, so i guess that the whole weekend will go to getting it in my hands and programming the short cuts. According to the digital picture, the 400 2.8L IS II is not bad with the 2xIII TC as far as IQ and AF is concerned.
I am thrilled about this, and I hope the eagles are there. The guy who runs this places food there for the wild animals, and he has seen them there every day he has been there this winter.
I am thinking that if the time is there, and I have secured some shots that I like, I would like to try the multiple exposure shot feature on the 1Dx, ... Could be cool