I've owned a 1D4 for about six years. When I got it, it replaced a 1D3 and was used alongside a 5D (classic) as my go-to sports camera. I shoot a lot of sports of my kids etc.
I replaced the 5D (classic) with a 5D Mark III about four years ago. So I've been running the 1D4 and 5D3 side by side for four years. My initial take four years ago was that the two cameras were close in AF performance, while the 1D has some obvious speed and robustness advantages.
I've also got a few newer lenses....the Sigma 120-300 Sport and the 70-200/2.8 IS II in this recent period. Anyway.....what I've been coming to to understand in the past year is that my 5D3 is just a better camera in regards to AF performance than the 1D4. Given some shifts in what and how I'm shooting I finally decided this year to let the 1D4 go. It's generating more misses in general for me, and the burst/buffer speed, while super nice, are not as much of a need.
So the point of this thread? I guess I'm just checking in to see if anyone else is seeing that the more recent AF systems are better for you. And I guess to some extent I feel a little funny letting the 1D go. I've had a 1D of some kind for the past eight years and there is a lot to like....but fundamentally I can get the shot now with the 5D3 and I just finally realized I just do not need to have two bodies sitting around (not counting my 5D classic which belongs to my daughter now and is the ultimate backup).