Brian, I know how much you love FF cameras. And yes, I never owned a FF, but I know enough people who own FF and who are amazing photographers. However, do their ISO 100 - 400 pictures look much better than mine? Only when they have a better composition,
They have an easier time obtaining shallow depth of field. An f/2.8 zoom on full frame has comparable depth of field to an f/1.8 prime with the same field of view. For portrait shots, this is important.
but in general it's very hard to distinguish a modern crop from a FF in good light. Yes, in low light a crop will have no chance compared to a FF. But then the question is why don't you use MF or even 4'x5' film?
Full frame is your best choice for shooting in low light. Current versions of MF cameras don't go past ISO1600 at all and to get the most out of them you really want to shoot at low ISO. They are designed for producing gallery size prints, not low light shooting. Same with film -- what type of film performs well at ISO6400 ?
However, and coming back to the topic - it is as true that for action the 5D II (which has an AF comparable to the 450D not the 60D) can't hold a candle to the 7D. Of course, if you are the perfect photographer and use MF on action shots and get everything right you still will get good pictures,
The 5DII does have a servo mode. It might not be as good as that on the 7D, but it is quite a bit better than manual focus.
but the 7D will have more keepers and get more interesting moments because of the highly superior burst rate. And not everyone wants everything centered in the picture (of course I can crop in post production, but with a 7D I can use an outer AF point and still have great performance).
The outer focus points are reasonably usable in one shot mode, especially if you are working with decent light. There is also focus and recompose, of course. Most of the cropping I do with my 5D shots is to make post hoc
revisions to composition. But I do not find that the AF system dictates my composition, when I need to make such revisions, it's either because I made an error, or because I was unable to get the composition I wanted (e.g. distance limited)
I bet that a pro with a 7D will get much superior sports pictures than a pro with a 5D II.
Sure, I don't think anyone is claiming that the 5D is a sports camera.
So, in the end I still believe that these cameras have different target audiences - 5D II for studio/portraits and 7D for sports/ birds/ moving animals/ moving kids...
You keep hammering away at this fallacy that the 5D is only usable for subjects that are either stationary or posing, but there are huge numbers of 5D series users photographing weddings and family pictures who would beg to differ.
For example, with kid shots -- you might get fewer keepers with a 5D series camera, but the keepers you get will be priceless. Again, having control over depth of field is very useful, especially shooting in busy (uncontrolled) environments where you can't stage the background to your liking.
And while kids do move around a lot, they also do sit still (sometimes), and when they are moving, they are not always running directly at the camera. The only knock against using a camera like the 5DII for taking shots of your kids is that it does perhaps seem like a massive overkill for that task.