I have two 5D2 bodies and love them. My only issue with the 5D2 is that in difficult lighting conditions, the AF can hunt around a bit. I mainly do event and wedding photography and naturally wouldn't want to miss an all-important shot. At my last shot which was a concert and reception, I did have difficulty at times with focusing issues. The concert was fine but I had some problem at the reception and at the arrival of the guests when I was using a 50/1.2L! While I also have a 580 ExII, I tend to shoot in available light pushing the ISO anywhere to 6400. I would be grateful for some advice as to whether it would serve me to swap one of my 5D2s for a 1D3 as I understand that the AF system on the 1D3 is perhaps more effective. With thanks in anticipation.