So today I went out to shoot some football games with my 5D2, and was really disappointed with the 5D2's ability to track subjects. A lot of my images would be really OOF. I know the 5D2's AF is nothing amazing, but I did walk away with some great keepers when I wasn't relying on the AI Servo and measly 4 FPS burst. I missed some great opportunities because the action would happen in between each frame. I guess naturally at this point I would be a bit annoyed with the speed aspect of the 5D2.
Anyway thats a bit of a back story. I basically shoot automotive subjects, 99% of the time, usually stationary for a shoot, however I am looking to branch out into other areas. I have been contemplating doing a direct swap with a 1D3 for my 5D2. I wrote down a list of Pros/Cons for each, and the Pros of the 1D3 severely out number the 5D2 and the 5D2's Cons out number the 1D3.
Yes I would be losing 11MP of resolution, however, I rarely print images, only when clients want them. I have enjoyed having the ability to use 21MP for both IQ and cropping and printing large 
I just wanted to see what everyone else would do in my situation. My idea is to swap out now, before 5D2 prices go even lower, and go for a 1D3 now, then buy back a FF body in the near future. I have used the 1D3 in my local camera shop and it's a beast of a camera. Just feel so proper to use, that maybe just maybe, I can let go of the FF for a while 
You didn't mention a budget
