So over the Thanksgiving weekend, I finally gathered the nerve to just let go of my 5D3 as I was offered a fair price for it. That, in conjunction with the deal for the 6D at $1400 pushed me into pulling the trigger on the swap out. Done and done.
Some things I'm struggling with, some not so much. Either way, I think the decision was the right one for me (for now).
Wondering if anyone else has given the same move some thought.
I haven't done exactly what you have done BUT I had the chance to shoot with a 5D3 for the day and now that I have, I won't buy one. I will keep my 7D.
The 5D3 is a great camera but not worth (at least to me) the $3400 price tag. After reading people's thoughts and reviews I was expecting a powerhouse of a camera, and it really wasn't. I just couldn't justify spending the money on it to upgrade. The 7D is a VERY fast camera and very hard to beat in that department. I shot BIF (birds, raptors exactly, in flight) with the 5D3 and got 10 times more blurry bird shots than I did with my 7D! (Yes I KNOW how to set up my camera for birds in flight, I am NOT new to this! Please don't waste your time telling me how I didn't know what I was doing... I always select the center point on AF and use AI Servo...) I was also using my own EF 70-300L on the 5D3. That lens is lighting fast on AF, so I know the fault wasn't with the lens.
Actually, for BIF, single center point is not the best AF option. The ideal setup, on both the 5D III and 7D, is to use at the very least center point expansion, but small zone works just as well if not better in some cases. The reason for this is due to the fact that even with steady hands, at long focal lengths the subject moves around a little bit in the frame, which can make detection of contrasty regions by the AF unit difficult. Just going to expansion mode does wonders for BIF tracking accuracy on both cameras, but more so with the 5D III as it's AF points are smaller than the 7D points (which are actually rather huge relative to the frame).
Small zone works even better on the 5D III, however it is less biased for the center points, which are more precise than the two columns of points on either side. On top of that, you need a slow to medium-slow tracking sensitivity (check custom functions), which will help mitigate focus jumping when momentary obstructions pass in front of the bird being tracked (the 7D and 5D III default to a moderately fast setting, meaning focus tends to jump off your subject to whatever is closer to the photographer...took me a bit to figure this out for the 7D when I first started BIF, and I kept getting clearly focused trees and telephone poles and the like in my continuous shooting of birds like raptors, pelicans, gulls, etc..)
I know a few people will say that I didn't give the 5D3 a chance to give it an honest opinion. Well, let me say this, I had (on loan) the 5D3 for a day and took well over 1000 photos AND was shooting with friends who OWNED the 5D3 and I was asking questions and they were gladly giving me pointers. By the time the day was over, I was so frustrated after shooting with it for a day and getting missed shot after missed shot. In contrast, when I upgraded from my 40D to my 7D, the transition was almost seamless. I had the 7D mostly figured out in just a few shots and was very happy with my decision. It was so much faster (in AF and fps) than my 40D that I was sorry I hadn't upgraded sooner! I learn more and more about it the more I shoot. Honestly? I had really been wanting a 5D3 so I know I was excited to give it a try. It just did not deliver enough goods to make me want to give up my 7D.
First, a couple thousand shots, especially with BIF, is maybe an hour of shooting (average burst of 5-6 frames, every 15-30 seconds or so...which is a fairly conservative estimate given that you can easily burn through the whole buffer for one longish BIF sequence, and fill a 32gb card with over 1200 shots in an hour of active shooting). In a couple hours of AI Servo action tracking photography, I can fill up a few CF cards, with bursts between five to twenty shots each (which is only a second or two worth of actual shooting.) If you had said you took 5000-8000 shots over a few of days, it would seem like you had more experience with the camera. A thousand shots with BIF doesn't feel anywhere remotely close to enough experience to actually get the hang of using the 5D III (in one years time, I took almost 80,000 shots with my 7D, the very vast majority of which were birds and BIF). Given what you have described, if you really did have all that trouble after being experienced with the 7D, then it honestly sounds like you might have even had a bad copy. Assuming it was properly configured as I mentioned above, the 5D III should be nailing birds in flight with tack sharp results like clockwork...to have such consistent problems focusing indicates either operator error or a defective copy.
I'd also point out that world renown professional photographers like Art Morris use the 5D III on a daily basis for bird and BIF work. With the proper skill, the 5D III is an extremely powerful tool for capturing action...just as powerful as the 7D, but with the potential to pack more pixels on subject...23% more on average.
It's all fine and dandy if you prefer your 7D. Nothing wrong with that. It just sounds like you are on a crusade to demonize the 5D III based on a rather fleeting "1000+" shots experience with it. It is a far more capable and effective camera than you are giving it credit for.