I currently have a 7D version 1 and am looking to get a second body. I primarily do perching bird and wildlife photography. I have a 600 F4, 400 5.6 and a 300 2.8 that are my go to lenses for this.
I'm trying to decide the pros and cons for the above bodies when used for my application. I even thought about finding a clean used 1D mkIV. A friend has the mk IV and really likes it but admits it's getting a little dated now. Is focus locking ability on the above bodies about equal amongst them or would one be better noticeably when it comes to low light conditions etc.? High frame rate is not a deal breaker for me and I don't do any large prints at this point. It seems initially that that having the ability to shoot full frame, 1.3 or 1.6 on the 5DS would be very nice but maybe I'm sacrificing something by having that option built in to that body?
Any opinions would be appreciated.